ALBERT

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-14, Ahead of Print.

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-16, Ahead of Print.

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-11, Ahead of Print.

Description: We report the preparation, crystallization, and solid state characterization of a new benzannulated phenalenyl radical; a distinctive feature of this molecular solid is the absence of any well defined conducting pathway(s). In the solid state, the radicals exist as π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The magnetic susceptibility measurement indicates that, in the solid state, the radical remains paramagnetic and the fraction of Curie spins is 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σ RT  = 0.5 × 10 −6  S/cm. The conductivity value is comparable with those of similarly packed phenalenyl based neutral radicals. Copyright © 2012 John Wiley & Sons, Ltd. A stable benzannulated phenalenyl based organic neutral radical has been reported in which we identify the features that limit the conductivity of organic molecular solids. The radical exists as a π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The radical remains paramagnetic and the fraction of Curie spin available 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σ RT  = 0.5 × 10 −6  S/cm.

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-19, Ahead of Print.

Description: Hydrolytic reactions of cyclic bis(3′-5′)diadenylic acid (c-di-AMP) have been followed by Reversed phase high performance liquid chromatography (RP-HPLC) over a wide pH range at 90 °C. Under neutral and basic conditions (pH ≥ 7), disappearance of the starting material (first-order in [OH − ]) was accompanied by formation of a mixture of adenosine 2′-monophosphate and 3′-monophosphate (2′-AMP and 3′-AMP). Under very acidic conditions (from H 0  = −0.7 to 0.2), c-di-AMP undergoes two parallel reactions (first-order in [H + ]): the starting material is cleaved to 2′-AMP and 3′-AMP and depurinated to adenine (i.e., cleavage of the N -glycosidic bond), the former reaction being slightly faster than the latter one. At pH 1–3, isomerization to cyclic bis(2′-5′)diadenylic acid competes with the depurination. Copyright © 2012 John Wiley & Sons, Ltd. Hydrolytic reactions of cyclic bis(3′-5′)diadenylic acid have been followed by RP-HPLC over a wide pH range at 90 °C. Under neutral and basic conditions, disappearance of the starting material was accompanied by formation of a mixture of adenosine 2′-monophosphate and 3′-monophosphate. Under acidic conditions, c-di-AMP undergoes the cleavage to 2′-AMP and 3′-AMP, depurination to adenine and isomerization to cyclic bis(2′-5′)diadenylic acid.

Description: The electrochemical behaviour of 13 chalcone analogues was systematically studied by means of cyclic voltammetry and chronoamperometry at a glassy carbon (GC), gold and platinum working electrodes using two different supporting electrolyte/solvent combinations. It was found that chalcone analogues can be easily oxidized at both GC and gold working electrodes, but not at a platinum electrode. Principal component analysis was further employed to reveal similarities/dissimilarities between oxidation potentials, chronoamperometric signals and ability of the compounds to scavenge the reactive oxygen species H 2 O 2 . The study reveals the inverse proportional relationship between the scavenging ability of H 2 O 2 , expressed as IC 50 , and chronoamperometric signal at 800 mV using gold as working electrode. Copyright © 2012 John Wiley & Sons, Ltd. The electrochemical properties of a series of antioxidant synthetic 2'-hydroxychalcone analogues, bearing a variety of substituents on both aromatic rings, were studied employing cyclic voltammetry and chronoamperometry. The ease of oxidation on glassy carbon and gold electrodes was found to be affected by the substituents present on the chalcone framework. Principal component analysis confirmed that there is a strong similarity between oxidation potentials, chronoamperometric signals and reactivity towards the reactive oxygen species H 2 O 2 , possibly deriving from the general oxidation capacity.

Description: photo credit to Harold Shapiro

Description: The organoaluminum mediated epoxide ring opening of epoxy alcohols is a key step in the oxirane-based approach for polypropionate synthesis. However, this reaction has shown unanticipated regioselectivities when applied to 2-methyl-3,4-epoxy alcohols. In order to gain mechanistic insight into the factors controlling the epoxide ring opening process, diastereomeric 2-methyl-3,4-epoxy alcohols were reacted with triethylaluminum in order to identify the aluminum complexes formed by these systems. Different epoxide–aluminum complexes were calculated using ab initio HF/[13s7p/11s5p] and B3PW91/6-31G** gauge-including atomic orbital (GIAO) methods and compared to the experimental NMR data. The calculated and experimental data correlates with the aluminum dimer complex (TIPSOCH 2 CH(OAlEt 2 )CH(CH) 3 CHCH(O)(AlEt 3 )) 2 (VIII) for the systems favoring the nucleophilic attack at the external C4 epoxide carbon, while an unusual trialuminum species TIPSOCH 2 CH(OAlEt 2 )CH(CH) 3 CHCH(O)(AlEt 3 ) 2 (X) is consistent with the systems favoring the internal C3 attack. The 27 Al NMR data established the tetracoordinated nature of the aluminum metal in all alkoxy aluminum intermediates, while the 13 C NMR data provided insight into the aluminum-oxygen coordination. The formation of the complexes was dictated by the stereochemical disposition of the substituents. These complexes are different from the generally accepted bidentate intermediates proposed for 2,3-epoxy alcohols and simpler 3,4-epoxy alcohols. Copyright © 2012 John Wiley & Sons, Ltd. Experimental and calculated NMR studies were performed using ab initio HF/[13s7p/11s5p] and B3PW91/6-31G** GIAO methods to rationalize the regioselectivities observed for the alane-mediated ring opening of diastereomeric 2-methyl-3-4-epoxy alcohols. The aluminum dimer complex VIII correlates with the systems that favor the attack at the C4 epoxide carbon, while trialuminum complex X showed a correlation with the systems that promote the attack at the C3 carbon.

Description: A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2-phenylpyridine) with various main group moieties in [Ir(ppy-X) 2 (acac)] (X = POPh 2 , SO 2 Ph, GePh 3 , OPh, OPh(CF 3 ) 3 , SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time-dependent density functional theory (TD-DFT) and Hartree–Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD-DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground- and excited-state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light-emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron-injection and electron-transporting features. Copyright © 2012 John Wiley & Sons, Ltd. The low energy transition of the considered cyclometalated iridium(III) phosphors is mainly metal-to-ligand charge transfer because the occupied orbitals consist mainly of a mixture of phenyl π- and Ir d-orbitals, while unoccupied orbitals are localized principally on ppy, with the predominant contribution being derived from the pyridyl π-orbitals.

Description: In this work, we present the optimized ground state geometrical structures, electronic excitation energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated Tce-CH3COCOOH and Tce-CH3C(OH)2COOH as well as their corresponding hydrogen-bonded dimers Tce-CH3COCOOH-H2O and Tce-CH3C(OH)2COOH-H2O through time-dependent density functional theory method. It is found that the intermolecular hydrogen bonds C=O···H-O are strengthened in the electronically excited states of the hydrogen-bonded dimers Tce-CH3COCOOH-H2O and Tce-CH3C(OH)2COOH-H2O, in that the excitation energies of the related excited states for the hydrogen-bonded dimers are decreased compared with those of the corresponding monomers. The calculated results are consistent with the rules that are first demonstrated by Zhao on the excited-state hydrogen bonding dynamics. Copyright © 2012 John Wiley & Sons, Ltd. In this work, DFT/TDDFT calculations were performed to the electronic excited-state hydrogen bonding dynamics of pyruvic acid and geminal-diol, 2,2-dihydroxypropanoic acid in aqueous solution. It was found that the intermolecular hydrogen bonds C=O···H-O will be significantly strengthened in the electronically excited states of the hydrogen-bonded dimers Tce-CH3COCOOH-H2O and Tce-CH3C(OH)2COOH-H2O upon photoexcitation.

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-12, Ahead of Print.

Description: Imine formation in aqueous solution of kanamycin A with pyridoxal 5'-phosphate and other aldehydes was studied by potentiometry, NMR spectroscopy and computational chemistry. It was found that imines are formed with yields near 100 % at pH 7 in equimolar reactant ratio. In order to identify the kanamycin amino groups involved in the reaction, a NMR spectroscopic study was conducted. The structures of possible imines formed between kanamycin and FURAN or PLP were optimized by molecular mechanics with the OPLS-2005 force field. The 1 H NMR spectra were calculated at the DFT-GIAO B3LYP/6-31G(d) level of theory for all structures and compared with the experimentally observed spectra. From these results a probable structure of the imines was proposed. The results obtained in this work show that kanamycin has the ability to form imine derivatives in high yields due to its anion recognition properties. Copyright © 2012 John Wiley & Sons, Ltd. Imine formation in aqueous solution of Kanamycin A with pyridoxal 5'-phosphate and other aldehydes was studied by potentiometry, NMR spectroscopy and computational chemistry. It was found that imines are formed with high yields at pH 7 in equimolar reactant ratio.

Description: The structure, relative energies, and bonding in morpholine(water) n ( n  = 1–4) clusters have been investigated at the Becke, three-parameter, Lee–Yang–Parr/6–311 + G(3df,2p)//Becke, three-parameter, Lee–Yang–Parr/6–311 + G(d,p) level of theory. Cooperative effects have been analyzed through the use of structural, energetic, and electron density indexes. Our analysis shows that these effects are crucial to trace the relative stability of the complexes formed. In all cases water molecules prefer to self-associate forming chains in which each individual molecule behaves as a hydrogen bond (HB) donor and HB acceptor. The chain so formed behaves in turn as HB donor and HB acceptor with respect to morpholine, being the most stable arrangements those in which the NH group of morpholine behaves simultaneously as HB donor and HB acceptor. Higher in energy lie complexes in which the HB acceptor continues to be the NH group, but the HB donor is a CH group, or alternative structures in which the HB acceptor is the ether-like oxygen of morpholine and the HB donor its NH group. Cooperativity increases with the number of solvent molecules, but there is a clear attenuation effect. Thus, whereas the additive interaction energy on going from dihydrated to trihydrated species increases by a factor of 3, this increase is about half on going from trihydrated to tetrahydrated complexes. Copyright © 2012 John Wiley & Sons, Ltd. The cooperative effects are crucial to trace the relative stability of the morpholine-(water) n ( n  = 1–4) clusters. In all cases water molecules prefer to self-associate forming chains in which each individual molecule behaves as a hydrogen bond donor and hydrogen bond acceptor.

Description: 13 C NMR spin–lattice relaxation times and nuclear Overhauser effects were measured at several temperatures for the methoxyl methyl carbon and the phenyl ring carbons in neat samples and in dilute cyclohexane solution for anisole, 4-methylanisole, and 4-chloroanisole. Similar measurements were made for 2-methylanisole, 2-methyl-4-bromoanisole, and 2,4,6-trimethylanisole in dilute cyclohexane solution. Density functional theory (DFT) computations were performed on anisole, 4-chloroanisole and 2,4,6-trimethylanisole to obtain the minimum energy structures and the potential energy barriers to the internal rotations of the methoxyl group. The shortest distance between a methoxyl methyl hydrogen and the ortho hydrogen in anisole is 1.920 Å. The DFT results point to steric interactions that arise thereof as the principal source of the energy barriers to the internal rotation of the methyl or of the methoxyl group. The carbon relaxation data are consistent with the existence of noncovalent intermolecular interaction, especially π − π stacking interaction. The nuclear magnetic resonance and DFT results are discussed with reference to the rotational characteristics of the methoxyl methyl and the anisotropy in the reorientational motion of anisole and its derivatives in dilute cyclohexane solution. Copyright © 2012 John Wiley & Sons, Ltd. In the solution state noncovalent interactions, especially p-p stacking, retard the reorientational motion of anisole and its derivatives, as revealed by 13C NMR relaxation data. The steric interactions between an ortho hydrogen and the methyl hydrogens of the methoxyl become the primary potential energy barrier which hinders the rotational motions in the methoxyl group.

Description: A new mechanism for the origin of multiple skeletal isomers observed in the cationic dimerization of 1-decene is proposed, and products that should form based on this mechanism are predicted. A protonated cyclopropyl intermediate appeared to form directly from combination of 2-decyl carbocation with 1-decene; formation of this intermediate did not appear to occur via ring closure of a branched secondary carbocation. The authors propose that rapid, repeated isomerizations of the protonated cyclopropyl intermediates lead to multiple skeletal isomers in decene dimers. The proposed mechanism can account for structures previously identified in mixtures of decene dimers and butene dimers. Copyright © 2012 John Wiley & Sons, Ltd. A new mechanism for rapid skeletal isomerizations of protonated cyclopropyl intermediates is discussed. Intermediates appeared to form by direct interaction of an alpha olefin with a secondary carbocation, during cationic oligomerization of alpha olefins. Model predicts structures of isomers present in polyalphaolefin mixtures.

Description: No abstract is available for this article.

Description: A theoretical study on the regioselectivity of 1,3-dipolar cycloaddition reaction between an uncommon dipole (thiocarbonyl S -imide) with cyclopent-3-ene-1,2-dione (DPh1) and methoxyethene (DPh2) has been carried out by means of several theoretical approaches, namely, activation energy, Houk's rule based on the frontier molecular orbital theory and density functional theory (DFT) reactivity indices. The calculations were performed at the DFT-B3LYP/6-31G(d) level of theory using GAUSSIAN 09. The present analysis shows that the 1,3-dipolar cycloaddition of thiocarbonyl S -imide with DPh1 and DPh2 has normal-electron demand and inverse-electron demand character, respectively. Moreover, the results obtained from energetic point view are in agreement with electronic approaches, and the Houk's rule is capable to predict true regioselectivity. Copyright © 2012 John Wiley & Sons, Ltd. 1,3-Dipolar cycloaddition of thiocarbonyl S-imide with cyclopent-3-ene-1,2-dione and methoxyethene has normal-electron demand and inverse-electron demand character, respectively. The results of activation energies, frontier molecular orbital energies, Gazquez-Mendez rule, Chattaraj's polar model and Houk's rule for prediction of favored regioisomers are in agreement with each other.

Description: The reduction of nine symmetric dicyanoaromatic radical anions by sodium amalgam in the presence of cryptand[2.2.2] was studied using cyclic voltammetry and using optical and electron paramagnetic resonance (EPR) spectroscopies in two aprotic solvents. All radicals are charge-delocalized (Class III) mixed valence species, as shown by the weak solvatochromism of their low-energy optical bands and by the vibrational structure exhibited by most of the bands. The maximum of the low-energy optical transition decreases logarithmically with the number of bonds ( n ) between cyano groups in a series of p-phenylene-bridged radicals, from p-phenyl ( n  = 5) to p-quaterphenyl ( n  = 17), although the energy of the latter lies higher than the value predicted by the linear regression. The energy of this band decreases linearly with the cos 2 value of the torsion angle between phenyl rings in the spectra of biphenyl-4,4′-dicarbonitrile radical anion and their methyl-substituted derivatives. The fact that charge delocalization is maintained in radicals with non-Kekulé bridges, with unusually large bridges and with bridges with highly twisted biphenyl systems suggests that cyano charge-bearing units have small reorganization energies and induce high electronic couplings through the bridges. Copyright © 2012 John Wiley & Sons, Ltd. Nine dicyanoaromatic radical anions were studied by visible/near infrared spectroscopy and found to be charge-delocalized mixed valence species, even the ones with bridges that are supposed to induce a small electronic coupling between cyanoaromatic units.

Description: The hydrolysis of 2-chloro-3,5-dinitropyridine by sodium hydroxide in the presence of micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and sodium dodecyl sulfate (SDS) has been studied. The reaction follows a consecutive reaction path involving the formation of a long-lived intermediate 4 and finally giving the product, 3,5-dinitro 2-pyridone 2 . The mechanism follows an addition of the nucleophile, ring opening and ring closure (ANRORC) reaction path. The rate constant was observed to be first-order dependent on [OH − ]. The rate of reaction increased on increasing [CTABr] and, after reaching to the maxima, it started decreasing. The anionic SDS micelles inhibited the rate of hydrolysis. The results of the kinetic experiments were treated with the help of the pseudophase ion exchange model and the Menger–Portnoy model. The added salts, viz . NaBr, Na-toluene-4-sulphonate, and (CH 3 ) 4 NBr on varying [CTACl] and [SDS] inhibited the rate of reaction. The various kinetic parameters in the presence and absence of salts were determined and are reported herewith. Copyright © 2011 John Wiley & Sons, Ltd. 2-chloro-3,5-dinitropyridine is hydrolyzed by sodium hydroxide to give 3,5-dinitro 2-pyridone. The reaction proceeds through ANRORC reaction mechanism with the formation of a long lived anion. Addition of CTABr micelles catalyzed the rate of hydrolysis, whereas SDS inhibited the rate of reaction. The observed results are explained on the basis of Menger–Portnoy model.

Description: The photochemistry of pivaloyl, benzoyl, 4-phenylbenzoyl, and 2-anthroyl azides has been studied using femtosecond (fs) time-resolved infrared (TRIR) and UV–vis spectroscopy and interpreted with the aid of computational chemistry. Density functional theory calculations revealed a significant difference in the nature of the lowest singlet excited state for these carbonyl azides. The lowest singlet excited states ( S 1 ) of p -phenylbenzoyl and 2-anthroyl azides are (π,π*) in nature, while the pivaloyl and benzoyl azides S 1 states involve ( n ,π*) excitations. Nevertheless, for all acyl azides studied here, a similar, and intense, IR band at about 2100 cm −1 has been detected in the ultrafast TRIR experiments following 270 nm excitation. These bands were shifted to lower energy by about 100 cm −1 relative to the N 3 stretching mode for the ground states of these azides. These 2100 cm −1 vibrational bands were assigned to the S 1 states of acyl azides in agreement with density functional theory calculations. The decay of the acyl azide S 1 states was described by bi-exponential functions. The fast component was attributed to the decay of the hot S 1 state and the longer component to the decay of the thermally relaxed S 1 state. A strong and broad transient absorption in the 350–650 nm spectral range was observed in the fs UV–vis experiments for p -phenylbenzoyl and 2-anthroyl azides. The carrier of this absorption also decayed bi-exponentially, and the time constants were in excellent agreement with those found in the fs TRIR experiments. The slow component of the S 1 state decay was found to be dependent on the solvent polarity. When the lifetime of the acyl azide S 1 state is substantially longer than the time constant for vibrational cooling of nascent (hot) isocyanate, the correlation between the S 1 decay and isocyanate formation was clear. The 270 nm excitation populates the S n ( n  ≥ 2) states of these acyl azides. It was established that a hot nitrene is produced more efficiently from both the S n and hot S 1 states than from the relaxed S 1 state of these acyl azides. Thus, time-resolved study provides direct experimental evidence that the S 1 state is the precursor of nitrene only when the S 1 state is pumped directly and when the S 1 state lifetime is longer than the time constant of vibrational cooling of the newborn nitrene. All of these results are consistent with the data obtained recently for 2-napththoyl azide. Copyright © 2012 John Wiley & Sons, Ltd. The photochemistry of pivaloyl, benzoyl, 4-phenylbenzoyl, and 2-anthroyl azides has been studied using femtosecond time-resolved infrared (TRIR) and UV–vis spectroscopy and interpreted with the aid of computational chemistry. The density functional theory calculations revealed a significant difference in the nature of the lowest excited state for these carbonyl azides. For all acyl azides studied here, a similar, and intense, IR band at about 2100 cm −1 has been detected in the ultrafast TRIR experiments following 270 nm excitation.

Description: An effective degradation reaction of CH 2 Cl 2 by bispidine (3,7-diazabicyclo[3.3.1]nonane, C 7 H 12 (NH) 2 , 1 ) is reported. The reaction starts as low as −20 °C and is quantitative with respect to 1 . The overall reaction implies nucleophilic substitution of chloride, followed by a series of cascading acid–base reactions, ending with the formation of two easily separable products, one being soluble and the other insoluble. The starting 1 , the intermediates, and the products show a variety of interesting solid-state structures, associated with plasticity, N–H⋯N and N–H⋯Cl⋯H–N hydrogen bonding, and polymorphism. Copyright © 2012 John Wiley & Sons, Ltd. Degradation of CH 2 Cl 2 by the parent bispidine starts as low as −20 °C. The overall reaction implies nucleophilic substitution, followed by a series of cascading acid–base reactions. The starting bispidine, intermediates, and products show a variety of interesting solid-state structures, associated with plasticity, N–H⋯N and N–H⋯Cl⋯H–N hydrogen bonding, and polymorphism.

Description: The reaction of PhCOCH 2 Cl with OH – gave the expected α-substituted alcohol (PhCOCH 2 OH) in addition to three dimer products. To clarify whether the substitution product is formed by direct S N 2 or via carbonyl addition, the reaction of PhCOCH 2 Cl and OMe – was examined. The reaction gave two products, PhCOCH 2 OH as the major product after acid hydrolysis and PhCOCH 2 OMe as the minor product. An electron-withdrawing substituent on the phenyl ring enhanced the overall reactivity and gave more alcohol than ether. It was concluded that the alcohol was formed via carbonyl addition-epoxidation route, whereas the ether was formed by the direct substitution route. Copyright © 2012 John Wiley & Sons, Ltd. The reaction of PhCOCH 2 Cl with NaOMe gave two products, PhCOCH 2 OH as the major product and PhCOCH 2 OMe as the minor product. An electron-withdrawing sustituent on the phenyl ring enhanced the overall reactivity and gave more alcohol than ether. The alcohol was formed via carbonyl addition-epoxidation route, whereas the ether was formed by the direct substitution route.

Description: A major challenge in the pursuit of dynamic materials is the dichotomy between reversible structure and electronic conjugation. Guided by the precedence for N -heterocyclic carbenes (NHCs) to dimerize, couple with electrophiles and bind to transition metals, we proposed that linearly opposed bis(NHC)s could, in a similar manner, afford unsaturated homopolymers, alternating copolymers, and metallopolymers. To realize these goals, we developed synthetic methods for accessing ditopic NHCs and investigated their propensities to undergo homopolymerization via dimerization and copolymerization via coupling with ditopic electrophiles or divalent transition metals. The materials obtained from these reactions were of relatively high molecular weight, exhibited electronic properties that were consistent with extensively delocalized systems, and in many cases, were found to be thermally reversible. In addition to expanding the scope of carbene chemistry, these polymers represent significant advancements towards the realization of reversible, conjugated polymers. Copyright © 2012 John Wiley & Sons, Ltd. The pursuit of structurally dynamic, conjugated materials based upon bis( N -heterocyclic carbenes) (NHCs) is highlighted. Synthetic methods for accessing ditopic NHCs were developed, and their propensities to undergo homopolymerization via dimerization and copolymerization via coupling with ditopic electrophiles or divalent transition metals were investigated. In addition to expanding the scope of carbene chemistry, these polymers represent significant advancements towards the realization of reversible, conjugated polymers.

Description: Stable nonplanar polyaromatic carbocation, [C 20 H 10 CH 2 Cl] + (1) having the chloromethyl group covalently bound to the hub site of corannulene was prepared by reaction of C 20 H 10 with CH 2 Cl 2 and GaCl 3 in the presence of SnCl 2 . The X-ray diffraction study of the resulting salt, [1]∙[(SnCl)(GaCl 4 ) 2 ], revealed the presence of two rotational isomers for 1 in the crystal lattice. In the solid state, a complex polymeric inorganic anion of the overall composition [(Sn 2 Cl 2 )∙(GaCl 4 ) 4 ] ∞ is formed with the cationic π -bowls being attached to its backbone. Both X-ray and nuclear magnetic resonance spectroscopic data of 1 indicate the sp 3 hybridization of the C-atom of corannulene at the attachment point. An electrochemical investigation of 1 and the series of related corannulene cations, [C 20 H 10 R] + (R = CH x Cl 3– x ( x  = 0–3) and CH 2 CH 2 Cl), was carried out to elucidate the electronic consequences triggered by the above changes. This study revealed that the surface decoration of corannulene core makes the reduction of the resulting [C 20 H 10 R] + species significantly more difficult (by about 0.3 V) with respect to the parent bowl. To evaluate the consequences of the observed one-electron reduction and conceivable but not seen second-electron reduction on the corannulene core, theoretical calculations at the density functional theory level have been carried out. Copyright © 2012 John Wiley & Sons, Ltd. Functionalized corannulene cations [C 20 H 10 R] + are prepared and investigated by single crystal X-ray diffraction, nuclear magnetic resonance and UV–Vis spectroscopies. Their first electrochemical study reveals that the reduction of cationic species is more difficult compared with the parent bowl.

Description: Acenes are polycyclic aromatic hydrocarbons consisting of linearly fused benzene rings. These compounds are currently the subject of great interest from both fundamental and applied perspectives, particularly for use in organic electronics. This review highlights the computational studies carried out to understand acene reactivity, their reaction mechanisms, and the relationship of the latter to acene length. Generally, as acene length increases, the reactivity of acenes increases, and a greater tendency towards a biradical mechanism is observed. For example, an interesting change in mechanism (from concerted to biradical) is observed for the reaction of acenes (benzene through pentacene) with molecular oxygen. A computational study of the addition of HCl (which behaves as an electrophile) and water (which behaves mostly as a nucleophile) to acenes revealed that acene reactivity increases along the series up to hexacene and remains constant from hexacene and above because of the biradical character of the ground state of higher acenes. Although the exothermicity of the addition of water and HCl to acene is similar, the activation barrier for the addition of water is significantly higher than that for HCl. There is a substantial substituent effect on the energy barriers for electrophilic and nucleophilic reactions. Phenyl substitution at the most reactive meso-carbon atoms of the central ring of acene blocks dimerization through this ring but does not efficiently prevent dimerization through other rings. With respect to the self-reactivity (such as dimerization, etc.) of acenes, a computational study showed that the preferred pathways are the formation of acene dimers via a central benzene ring and the formation of acene-based polymers. Interestingly, longer acenes are predicted to self-react to form polymers, rather than acene dimers, as the thermodynamically preferred product. These findings invite experimentalists to reinvestigate the dimerization of long unsubstituted acenes. Given that computational studies directly relate to the gas phase reactivity of acenes, whereas long acenes find application in organic semiconductor devices as solids, the next research challenge is to obtain an understanding of the solid state reactivity of long acenes. Copyright © 2012 John Wiley & Sons, Ltd. The study of acene reactivity is important for basic understanding of aromatic and conjugated systems and can guide efforts to design stable acene derivatives for electronic applications. The current review summarizes recent computational studies of acene reactivity towards nucleophilic and electrophilic additions, oxidation by molecular oxygen, and dimerization. Generally, as acene length increases, reactivity increases, and often, change in mechanism with a greater tendency towards a biradical mechanism is observed.

Description: How does the endo C–F bond influence the excess electron binding motif? For lithium-doped endohedral perfluorofullerenes with endo C–F bonds, under both internal-push (from exo C–F bonds) and external-push (from endo C–F bonds) electron effects, the singly occupied molecular orbital electron cloud of the sphere-like Li···F 8 @C 60 F 52 ( D 2 ) is partially dispersed within the σ p–s antibonding orbital of endo C–F bonds and the space between C δ+ –F endo δ– double electric layers, which makes Li···F 8 @C 60 F 52 have partial excess electron (electride characteristics) and partial lithium salt characteristics, while in the tube-like Li···F 2 @C 60 F 58 ( C s ), as the Li is changing from approaching F to keeping away from F and to approaching another one, the singly occupied molecular orbital electron cloud is mainly dispersed from within the p orbital of the short endo C–F bond to within the middle of the two F atoms and again to within the p orbital of the short endo C–F bond, which indicates an evolution from lithium salt characteristic to excess electron characteristic, and again to lithium salt characteristic. Copyright © 2012 John Wiley & Sons, Ltd. Evolution of excess electron binding motifs in different lithium-doped endohedral perfluorofullerenes with endo C–F bonds.

Description: We report the effect of transition metal deposition on the conductivity of single-walled carbon nanotube (SWNT) networks. The slow evaporation of small amounts of highly mobile transition metal atoms significantly reduces the resistance of SWNT thin films; we suggest that Cr, Fe, and Ti atoms form bis-hexahapto complexes at the SWNT sidewalls, thereby bridging adjacent carbon nanotubes and reducing the inter-nanotube junction resistance. Copyright © 2012 John Wiley & Sons, Ltd. We report the effect of transition metal deposition on the conductivity of single-walled carbon nanotube (SWNT) networks. The slow evaporation of small amounts of highly mobile transition metal atoms significantly reduces the resistance of SWNT thin films; we suggest that Cr, Fe, and Ti atoms form bis-hexahapto complexes at the SWNT sidewalls, thereby bridging adjacent carbon nanotubes and reducing the inter-nanotube junction resistance.

Description: Air-tolerant 2,4-bis(2,4,6-tri- t -butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl singlet biradicals can be prepared by utilizing the unique reactivity of a kinetically stabilized P≡C triple bond compound. In this procedure, we studied the spectroscopic properties of a fundamental unsymmetrical P-heterocyclic biradical containing both PEt and PMe moieties, and the effects of the PCH 2 OMe group in relation to the stability of the P-heterocyclic biradical skeleton. The experimentally observed nuclear magnetic resonance and photo-absorption parameters of 1-ethyl-3-methyl-2,4-bis(2,4,6-tri- t -butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl were discussed based on our previous findings and density functional theory calculations, suggesting particular structural characteristics of the P-heterocyclic biradical skeleton and aromatic substituent effects on the sp 2 -C atoms in the 4-membered ring. Introduction of the methoxymethyl group in the P 2 C 2 biradical moiety gave more stabilized 1,3-diphosphacyclobutane-2,4-diyl derivatives. In comparison with considerably unstable biradicals bearing propargyl substituents, relatively higher lowest unoccupied molecular orbital energies suggest reluctant oxidation of the P-heterocyclic skeleton. Copyright © 2011 John Wiley & Sons, Ltd. UV-Vis photo-absorption properties for air-tolerant 1,3-diphosphacyclobutane-2,4-diyls as singlet biradicals indicate that employed sterically bulky aromatic substituents such as Mes* on the sp 2 -C atoms substantially conjugate with the cyclic skeleton to protect the biradical moiety effectively. The PR groups control the biradical stability by altering the electronic structures of the particular 4-membered heterocyclic system.

Description: The 1 H NMR titration method is used to investigate the association of some unsaturated alcohols with pyridine in benzene. The association constant for allyl alcohol (2-propen-1-ol) is slightly higher than for alkanols, but putting one methylene group between the OH and vinyl group completely eliminates this enhancement. In alkynols both the OH and ≡CH protons associate with pyridine. Here, the effects of chain-lengthening on the association constant are irregular. Values for alkynols and some alcohols with hetero-atom substituents are lower than expected on the basis of a Taft polar constant (σ*) correlation of alkanol association constants and of a correlation with the p K a ’s of the corresponding carboxylic acids. It is suggested that stabilization of the ground state by OH/π interactions is responsible for these low association constants. Small increases in the NMR shifts of the OH protons in the 3-carbon and 4-carbon alkenols and alkynols can also be attributed to OH/π interactions, but the 5-carbon analogues have shifts as low as alkanols. Copyright © 2011 John Wiley & Sons, Ltd. Through-bond enhancement of association constants by electron attractors are offset by through-space OH/p interactions, which show up in the 1H NMR spectra of some alkenols and alkynols.

Description: Photoinduced reactions of 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4- f ]quinoline-8-carboxylic acid (SeQCA) were investigated in alkaline media (aqueous NaOH solutions) by electron paramagnetic resonance (EPR) spectroscopy, following the in situ formation of paramagnetic species. According to UV–Vis and nuclear magnetic resonance investigations, protonation (pH ≈ 11) and deprotonation (pH ≈ 13) of the imino hydrogen of the 4-pyridone moiety has to be considered, reflected also in the different EPR spectra observed upon irradiation. Photoinduced generation of radicals was found only for carboxylate substituted SeQCA; other studied selenadiazoloquinolone derivatives, together with those substituted at the C(8) position (R = H, COOCH 2 CH 3 , COOCH 3 , COCH 3 or CN), did not generate paramagnetic species during exposure. Consequently, photodecarboxylation was suggested as the decisive step, accompanied by the decomposition of the selenadiazole ring, resulting in the formation of ortho -hydroxylate anions. EPR parameters elucidated from experimental EPR spectra obtained at pH ≈ 11 and pH ≈ 13 indicate the formation of oxygen-centered radicals at the decarboxylated 4-pyridone ring. EPR spin trapping experiments with nitromethane confirmed a very effective photoinduced electron transfer from all the selenadiazoloquinolones investigated. Copyright © 2011 John Wiley & Sons, Ltd. Photoexcitation of 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4- f ]quinoline-8-carboxylic acid in alkaline aqueous solutions results in the generation of two different radicals as monitored by in situ electron paramagnetic resonance spectroscopy, reflecting the protonation (pH ≈ 11) and deprotonation (pH ≈ 13) at the imino hydrogen of the 4-pyridone moiety. The reaction mechanism proposes photodecarboxylation, conversion of selenadiazole ring in ortho -hydroxylate substructure, as was evidenced in 17 O enriched water, and formation of oxygen-centered radicals on decarboxylated 4-pyridone ring.

Description: The photochemistry of 2,4,6-triazido-3,5-difluoropyridine 21 was investigated by matrix infrared and electron paramagnetic resonance spectroscopies. Ultraviolet irradiation (〉260 nm) of 21 results in the formation of 3,5-difluoropyridyl-2,4,6-trinitrene 26 in yields high enough for characterization by infrared spectroscopy. The experimental infrared spectrum is in good agreement with density functional theory calculations. Under similar conditions, a very strong electron paramagnetic resonance spectrum of septet trinitrene 26 was obtained. Shorter irradiation times resulted in more complex product mixtures containing, in addition, mononitrenes and dinitrenes. Surprisingly, azirines and keteneimines, the typical photoproducts of arylnitrenes, were not observed. Copyright © 2011 John Wiley & Sons, Ltd. UV irradiation (〉260 nm) of 2,4,6-triazido-3,5-difluoropyridine results in the formation of 3,5-Difluoropyridyl-2,4,6-trinitrene in yields high enough for characterization by IR spectroscopy. The experimental IR spectrum is in good agreement with DFT calculations. Under similar conditions a very strong EPR spectrum of septet the trinitrene was obtained. Shorter irradiation times resulted in more complex product mixtures containing in addition mononitrenes and dinitrenes. Surprisingly, azirines and keteneimines, the typical photoproducts of arylnitrenes, were not observed.

Description: The mechanisms of the single and double Mannich reactions between acetaldehyde and N-Boc imines are clarified by density functional theory calculations. For single addition of Mannich reaction, the energy difference between the transition states of different configurations correspond to an enantiomeric excess value of 90.58% (without solvent) and 98.46% (in acetonitrile) in favor of the (S)-configuration product. For bis-addition of Mannich reaction, the calculated enantiomeric excess value is 95.02% (without solvent) and 98.57% (in acetonitrile) in favor of the (S, S)-configuration product. These calculated results are in good agreement with the experimental results. The calculations clearly demonstrate that the hydrogen-bonding determine the stereochemistry of the reactions. Copyright © 2012 John Wiley & Sons, Ltd. DFT calculations demonstrate that the single and double Mannich reactions between acetaldehyde and N-Boc imines lead to the formation of the (S)-configuration and (S, S)-configuration products, respectively; the hydrogen-bonding determine the stereochemistry of the reactions and the solvent employed play an important role in determining the reaction rate and enantioselectivity.

Description: Electrochemical oxidation of 2,3-dihydroxypyridine in aqueous phosphate buffer solution at a glassy carbon electrode has been studied using cyclic voltammetry and controlled potential coulometry. The results indicate that oxidation of 2,3-dihydroxypyridine on glassy carbon electrode shows an irreversible feature in aqueous solution. This data indicates that the electrochemically generated pyridindione is unstable and via an oxidative conversion pathway converts to a novel highly oxygenated heterocyclic compound. By means of the obtained electrochemical data, an efficient, one-pot method for the synthesis of this heterocyclic compound based on the oxidative cyclization of 2,3-dihydroxypyridine under green conditions, and in a good yield and purity is described. Copyright © 2011 John Wiley & Sons, Ltd. Electrochemical oxidation of 2,3-dihydroxypyridine in aqueous solutions shows an irreversible process. The electrochemically generated pyridindione via an oxidative conversion pathway converts to a highly oxygenated heterocyclic compound. In this work, a green method for the synthesis of a novel heterocyclic compound is described.

Description: Exploratory computational studies on annulenes with planar, Möbius, and two-twist topologies have resulted in new mechanisms to explain facile thermal configuration change ( cis-trans isomerization) for medium-sized annulenes ([12]- to [16]annulene). Möbius π-bond shifting through both aromatic and antiaromatic transition states, two-twist π-bond shifting, and planar nondegenerate π-bond shifting can all be invoked to explain experimental results. Moreover, a simple bond-shift rule, which is based on the change in number of trans C C double bonds (Δ trans ), was developed that predicts the topology of the transition state(s) necessary to effect the desired cis-trans isomerization. The bond-shift rule was also applied to configuration change in dehydro[12]annulene. Finally, extensive investigation of the [14]annulene hypersurface revealed that numerous Möbius minima exist within 10 kcal/mol of the global minimum. Copyright © 2012 John Wiley & Sons, Ltd. Facile thermal configuration change in annulenes and dehydroannulenes is explained by π-bond shifting. According to the bond-shift rule, these reactions occur via planar, Möbius, or two-twist conformations.

Description: The basicity of a series of sulfonamides and carboxamides with respect to protonation and hydrogen-bonded complex formation with phenol was investigated by calculations using the Becke three-parameter hybrid functional combined with Lee–Yang–Parr correlation functional with the 6-311G** and 6-311++G** basis sets and by infrared spectroscopy. The effect of fluorinated substituent was studied for the two series. The proton affinity of nitrogen in sulfonamides is higher than oxygen, in contrast to carboxamides, which are protonated at oxygen. The phenyl group in benzenesulfonamide increases the basicity of both heteroatoms, but more strongly of the nitrogen, whereas in benzamide the effect on the two heteroatoms is about the same. The CF 3 group equally decreases the basicity of nitrogen and oxygen atoms in sulfonamides and carboxamides. The second fluorinated substituent decreases the basicity of oxygen in (CF 3 CO) 2 NH more strongly than of nitrogen. For sulfonamides, the same effect results in the reverse of the center of basicity from nitrogen in (MeSO 2 ) 2 NH to oxygen in (CF 3 SO 2 ) 2 NH. All studied carboxamides give H-complexes via the carbonyl oxygen, whereas for sulfonamides two types of H-complexes, with the OH···N and OH···O=S, were found theoretically, the latter being more stable. The exception is bisimide (CF 3 SO 2 ) 2 NH, for which only the OH···O=S complex is stable. Experimentally, only the oxygen-bound complexes are observed. Analysis of the natural charges revealed an ‘abnormal’ increase of the electron density on the NH group by electron-acceptor substituents in CF 3 SO 2 NHR, which was explained using the natural bond orbital analysis by loosening of the S–N bond because of orbital interactions with the σ* S−N orbital. Copyright © 2012 John Wiley & Sons, Ltd. The basicity of sulfon- and carboxamides with respect to protonation and H-bonding was studied theoretically and experimentally. spectroscopy. Unlike carboxamides, the proton affinity of nitrogen in sulfonamides is higher than of oxygen. Carboxamides give H-complexes via the carbonyl oxygen, whereas for sulfonamides H-complexes with OH···N and OH···OS H-bonds were found, the latter being more stable. Experimentally, only the O-bound complexes are observed.

Description: Several transition metal complexes based on 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (DTE) bearing terpyridine (TPY) have been designed and synthesized. Furthermore, the photochromism of the free ligand and the influence of transition metal moieties on the photochemical properties have been thoroughly characterized by monitoring the changes in their UVvis spectra. Compounds 3–6 all display excellent response to UV irradiation, especially Co complex 5 with optimum sensitivity that took only 5 s to reach photostationary state. The photochromic properties of DTE unit have been found to be strongly influenced by the bridging transition metals, as complexes 4 (L–Zn–L) and 6 (L–Ru–L) exhibit much better photochromic properties in tetrahydrofuran solution than complex 5 (L–Co–L) and the free ligand 3 (L). It is worth noting that the optical/chemical thermal stabilities of photochromic compounds 3–6 are all greatly improved after the precursor functionalized with TPY and further coordinated with metal ions. Copyright © 2012 John Wiley & Sons, Ltd. Several transition metal complexes based on 2,3-bis(2,4,5-trimethyl-3-thienyl)-maleic anhydride (DTE) bearing terpyridine (TPY) have been designed and synthesized. The photochromic properties of DTE unit have been found to be strongly influenced by the bridging transition metal. It is worth noting that the chemical thermal stabilities of these photochromic compounds were greatly improved after functionalized with TPY and further coordinated with metal ions.

Description: In this article, a series of Hantzsch 1,4-dihydropyridines with different substituted aryl groups were synthesized and its spectral data obtained by UV–Vis absorption and fluorescence emission spectroscopies in solution. The dihydropyridines present absorption located around 350 nm and fluorescence emission in the blue–green region. A higher Stokes' shift could be observed for the derivative 3b because of an intramolecular charge transfer in the excited state from the dimethylaniline to the dihydropyridine chromophores, which was corroborated by a linear relation of the fluorescence maxima (ν max ) versus the solvent polarity function (Δ f ) from the Lippert–Mataga correlation. A comparison between the experimental data and time-dependent density functional theory-polarizable continuum model calculations of the vertical transitions was performed to help on the elucidation of the photophysics of these compounds. For these calculations, the S 0 and S 1 states were optimized using Becke, three-parameter, Lee–Yang–Parr/6-31 G* and Configuration Interaction Singles/6-31 G*, respectively. The predicted absorption maxima are in good agreement with the experimental; however, the theoretical fluorescence emission maxima do not match the experimental, which means that the excited specie cannot be related to neither a locally excited state nor to an aromatized structure. Copyright © 2012 John Wiley & Sons, Ltd. A series of Hantzsch 1,4-dihydropyridines with different substituted aryl groups were synthesized and its spectral data obtained by UV–Vis absorption and fluorescence emission spectroscopies in solution. The dihydropyridines present absorption located around 350 nm and fluorescence emission in the blue–green region. A higher Stokes' shift could be observed for the derivative 3b because of an intramolecular charge transfer in the excited state from the dimethylaniline to the dihydropyridine chromophores. Time-dependent density functional theory-polarizable continuum model calculations of the vertical transitions were performed to help on the elucidation of the photophysics of these compounds. The predicted absorption maxima are in good agreement with the experimental; however, the fluorescence emission theoretical results do not match the experimental, which means that the excited specie cannot be related to neither a locally excited state nor to an aromatized structure.

Description: Atmosphere-Ocean, Volume 0, Issue 0, Page 1-9, Ahead of Print.

Description: Reaction of mineral acids with a cyclic macromolecule containing a secondary alcohol produces ammonium, phosphonium, thiophene, and amide adducts via a carbocation intermediate. X-ray crystallography confirms the structures of the products, including those when two competing nucleophiles are present. A reactivity series that mirrors the nucleophilicity index, where reactivity decreases in the order thiophene 〉 pyridine 〉 primary amides 〉 alkyl nitriles 〉〉 aromatic nitriles (unreactive), results. Addition of metal ions to ammonium adducts dissolved in acetonitrile produces secondary amides via the Ritter amide synthesis. Copyright © 2012 John Wiley & Sons, Ltd. Reaction of acid with a cyclic macromolecule containing a secondary alcohol produces ammonium, phosphonium, thiophene and amide adducts where reactivity decreases in the order: thiophene 〉 pyridine 〉 primary amides 〉 alkyl nitriles 〉〉  aromatic nitriles (unreactive).

Description: The solvent dependency of the ground-state distribution as well as the electrochemical switching behavior in a redox-active bistable donor–acceptor [2]catenane, containing bisthiotetrathiafulvalene (STTFS) and 1,5-dioxynaphthalene (DNP) recognition sites incorporated within a macrocyclic polyether encircled by the cyclobis(paraquat- p -phenylene) (CBPQT 4+ ) ring, has been investigated. There are two translational isomers: (i) the ground-state co-conformation (GSCC) in which the CBPQT 4+ ring encircles the STTFS unit and (ii) the metastable-state co-conformation (MSCC) in which the CBPQT 4+ ring encircles the DNP unit. 1 H NMR spectroscopy indicates that the ground-state distribution of GSCC to MSCC varies from approximately 1:1 in MeCN to 7:1 in MeCN : H 2 O (1:1, v/v) at 283 K. The reversible electrochemical switching behavior of the [2]catenane was confirmed by 1 H NMR and UV−Vis spectroscopies, as well as by cyclic voltammetry (CV). Additionally, variable scan-rate CV studies were compared with simulated CV data and show that the ground-state distribution of GSCC to MSCC is about 30:1 in MeCN : H 2 O (1:1, v/v) at 298 K. With the assistance of isothermal titration calorimetry of model compounds, it was found that the changing ground-state distribution in differing solvent systems is driven entropically rather than enthalpically. Copyright © 2012 John Wiley & Sons, Ltd. The solvent dependency of the ground state distribution and the electrochemical switching behavior in a redox-active bistable donor-acceptor [2]catenane, containing bisthiotetrathia fulvalene (STTFS) and 1,5-dioxynaphthalene (DNP) recognition sites incorporated within a macrocyclic polyether encircled by the cyclobis(paraquat-p-phenylene) (CBPQT 4+ ) ring, has been investigated. In aqueous solvent, CBPQT 4+ prefers to reside upon the STTFS unit, while in organic solvent the cyclophane shows little selectivity between the two stations. Entropy, rather than enthalpy, drives the changing ground-state distribution in differing solvent systems.

Description: Density functional theory calculations were performed on alkenols and alkynols at the PBE1PBE/6-311 + G(d,p) level with the inclusion of solvent (benzene) effects by the integral-equation-formalism polarizable continuum model (IEFPCM). For the smaller molecules, conformers in which the OH group is in the vicinity of the double or triple bond are preferred, but this preference falls as the alkyl chain is lengthened. The solvent effect on the relative Gibbs energies of different conformers is irregular, and in only two cases, 3-buten-1-ol and 3-butyn-1-ol, is there marked levelling. Gauge-including atomic orbital calculations, based on the PBE1PBE/6-311 + G(d,p) geometries but using a larger basis set, cc-pVTZ, give nuclear magnetic resonance shifts for all the protons in each conformer. Overall shifts are calculated by weighing these according to the conformer population. Calculated values are well correlated with experimental data from high-dilution spectra in the same solvent, ranging from about 0.4 to 5.8 ppm, with a slope of 1.09 ± 0.01. Calculations on some alcohols with hetero-atom substituents confirm that these also prefer gauche (synclinal) conformers in the gas phase, with a less marked preference in benzene. The nuclear magnetic resonance shifts, however, are calculated to be on average over 0.8 ppm higher than observed. Copyright © 2011 John Wiley & Sons, Ltd. 1 H NMR shifts and the relative populations are calculated for all conformers of 10 alkenols and alkynols in benzene to give overall shifts which correlate well with experimental data.

Description: An experimental approach was developed to determine the intrinsic thermolysis rate constants of the central carbon–carbon bond during the dl / meso isomerization of diethyl 2,3-dicyano-2,3-di( p -substituted phenyl)succinates (G=H, Me, OMe, Cl, and NO 2 ) at temperatures ranging from 80 to 120 °C. The obtained rate constants are significantly affected by the polarity of the para substituents, in sharp contrast to their negligible effects on the dl / meso isomerization equilibrium constants. Moreover, the substituent effects on the activation enthalpies can be linearly correlated with the Hammett substituent resonance constants and the homolytic dissociation enthalpies (bond dissociation energies) of the benzylic C–H bonds of ethyl 2-cyano-2-( p -substituted phenyl)acetates. Copyright © 2011 John Wiley & Sons, Ltd. An experimental approach was developed to determine the intrinsic thermolysis rate constants of the central carbon-carbon bond during the dl/meso isomerization of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates (G = H, Me, OMe, Cl, and NO 2 ) at temperatures ranging from 80 to 120 _C. The obtained rate constants are significantly affected by the polarity of the para substituents, in sharp contrast to their negligible effects on the dl/meso isomerization equilibrium constants.

Description: A new electrochemical procedure for the electrocatalytic dimerisation of benzoyl chloride in ionic liquid, 1-butyl-3-methylimidazoliumtetrafluoborate, to benzil was investigated for the first time. The electrochemical behavior of benzoyl chlorides in BMIMBF 4 was studied by cyclic voltammetry with a reduction peak at −1.2 V (vs Ag). The electrolysis experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, creating benzil at a moderate yield (51%). The results showed that the yields were strongly affected by various factors: temperature, working potential, electrode material. Moreover, the ionic liquid was successfully recycled for this reaction. Copyright © 2011 John Wiley & Sons, Ltd. A new electrochemical procedure for the electrocatalytic dimerisation of benzoyl chloride in ionic liquid, 1-butyl-3-methylimidazoliumtetra fluoborate (BMIMBF 4 ), to benzil was investigated for the first time. The synthesis was carried out under mild conditions, without resorting to the use of toxic solvents and catalysts. Benzil could be prepared in moderate yields (51%) under optimized conditions. Moreover, the ionic liquid was successfully recycled.

Description: Quantum chemical calculations have been performed to explore the mechanism of intramolecular cyclization of 2-benzyloxyphenyl trimethylsilyl ketone (acylsilane) to give the benzofuran derivatives stereoselectively. This reaction involves a formation of siloxycarbene intermediate and a C–H bond insertion of siloxycarbene. The comparative studies on three possible insertion of siloxycarbene show that the concerted insertion of siloxycarbene into C–H bond (pathway a), which needs overcoming an energy barrier of 45.1 kcal/mol, is the most unlikely pathway, and the stepwise insertion of siloxycarbene without spin multiplicity change (pathway c) is energetically more favorable than the stepwise insertion of siloxycarbene with spin multiplicity change (pathway b). More importantly, this work can provide an insight into the stereoselectivity in this reaction in atomic molecular level. The formation of siloxycarbene is calculated to be endergonic by 22.9 kcal/mol with an energy barrier of 30.2 kcal/mol, being the rate-determining step of the whole process. Copyright © 2011 John Wiley & Sons, Ltd. Three possible cyclization mechanisms of 2-benzyloxyphenyl trimethylsilyl ketone are comparatively investigated using quantum chemical method in this work. Our calculations show that 2-benzyloxyphenyl trimethylsilyl ketone firstly undergoes a 1,2-Brook rearrangement to give siloxycarbene, and siloxycarbene is then most likely to stepwise insert into the C–H bond without spin multiplicity change to stereoselectively provide the benzofuran derivatives, giving a satisfactory explanation on the experimental findings.

Description: We have undertaken an experimental and computational study of the structural properties of a few alkylfluoride–BF 3 complexes (RF′–BF 3 ), which are proposed intermediates in a certain class of Friedel–Crafts reactions. Using density functional theory and second-order Møller–Plesset calculations, we have obtained gas-phase structures, frequencies, and B–F′ bond potentials for CH 3 F–BF 3 , (CH 3 ) 2 CHF–BF 3 , and (CH 3 ) 3 CF–BF 3 . All the complexes are weakly-bonded in the gas phase, with B–F′ distances (X3LYP/aug-cc-pVTZ) of about 2.4 Å and binding energies (MP2/aug-cc-pVTZ) ranging from 5.4 and 6.7 kcal/mol. Accordingly, gas-phase bond potentials are relatively shallow and flat for these complexes. However, even though the inner walls of the potentials are rather soft (the energies rise by only about 5 to 10 kcal/mol between 2.4 and 1.6 Å), we observe no global or local minima at short B–F′ distances. For the (CH 3 ) 2 CHF–BF 3 and (CH 3 ) 3 CF–BF 3 potentials in dielectric media, we do observe a distinct flattening along the inner wall, which results in shelf-like region near 1.7 Å, but this feature is not a true local minimum. We have also obtained low-temperature infrared spectra of the (CH 3 ) 2 CHF–BF 3 complex in solid neon, and the frequencies agree quite favorably with those obtained via computations, which validates the computational assessment of the gas-phase complexes. Copyright © 2011 John Wiley & Sons, Ltd. The structural and energetic properties of a few Freidel-Crafts intermediates (alkyl-fluoride - BF3 complexes) have been characterized via computations and infrared spectroscopy. These complexes are weakly-bonded, with long intermolecular B-F' distances, and the alkyl substituents exhibit little or no carbocation character. The structures that correspond to points along the inner wall of the B-F' bond potential (1.4 to 1.6 Å) show some additional carbocation character, but these are predicted to lie at significantly higher energies, even in bulk, dielectric media.

Description: 2-(Pyridin-2-yl)furan-3-ol (PYFO, T1) and (2 E )-2-(pyridin-2(1 H )-ylidene)furan-3(2 H )-one (PYFO, T2) were considered to study their tautomerism interconversions, relative rotations of rings, OH bond rotations, and possibility of crossing between those energy surfaces using density functional theory methods at the Becke, three-parameter, Lee–Yang–Parr/6-311++G** level of theory. The optimized structures of both tautomers and the transition state of tautomerism are completely planar. A study of tautomerism in PYFO shows that T1 tautomer is about 24.38 kJ/mol more stable than T2. The rate constants of tautomerism interconversion for converting T1 to T2 is 1.98 × 10 8  M –1  s –1 and for converting T2 to T1 is 3.70 × 10 12  M –1  s –1 at room temperature that show the possibility of this tautomerism with high rate at ambient temperature. Rotation of OH bond in T1 shows two minimum (at 0° (global minimum) and 180° (local minimum)) and a transition state at 110° (and 265°) with 47.10 kJ/mol barrier energy. Relative rotation of rings shows global minimum at 0° for both tautomers and local minimum at 154° and 206° for T1 and 180° for T2. The barrier energy for ring rotation of T1 was observed at 90° and 270° with 63.69 kJ/mol height and for T2 was observed at 120 with 170.86 kJ/mol height. Interestingly, the energy levels of ring rotations for T1 and T2 are the same and crossing between them was observed. Therefore, although these two potentials do not have the same symmetries, because of the crossing between their energy level, crossing is not avoided. Copyright © 2011 John Wiley & Sons, Ltd. 2-(Pyridin-2-yl)furan-3-ol (PYFO, T1) and (2 E )-2-(pyridin-2(1 H )-ylidene)furan-3(2 H )-one (PYFO, T2) were considered to study their tautomerism interconversions, relative rotations of rings, OH bond rotations, and possibility of crossing between those energy surfaces. The energy levels of ring rotations for T1 and T2 are the same and crossing between them was observed. Therefore, although these two potentials do not have the same symmetries, because of the crossing between their energy level, crossing is not avoided.

Description: Hydroxy-9,10-anthraquinones resemble anthracycline-based anticancer drugs. By varying the pH of the solution, the proton dissociation constants of 1,2,5,8-tetrahydroxy-9,10-anthraquinone (THAQ) were determined. Interaction of THAQ with calf thymus DNA (ct DNA) was studied by UV–Vis spectroscopy to determine the overall binding constant and site size of interaction. The binding constant values (~10 4 ) for THAQ interacting with ct DNA at different pH were an order less than that known for anthracyclines. From knowledge of the overall binding constants at different pH values and the first pK of THAQ, the contribution of each form (neutral and monoanionic) towards overall binding with ct DNA could be obtained under physiological conditions. Hence, knowing the contributions of the neutral and monoanionic forms, it now becomes possible to know the overall binding constant for an interaction of THAQ with ct DNA at any pH. The calculated parameters help in understanding the role of the negative charge on the monoanionic form during interaction and suggests suitable chemical modifications that could prevent the development of such negative charges. This could lead to an increase in binding of THAQ to ct DNA. The study also helps to recognize the importance of sugar units in anthracycline anticancer drugs in DNA interaction. Copyright © 2011 John Wiley & Sons, Ltd. 1,2,5,8-tetrahydroxy-9,10-anthraquinone (THAQ) mimics physicochemical and biophysical characteristics of anthracycline anticancer drugs. Binding of THAQ to calf thymus DNA was comparable to anthracycline drugs but slightly weaker. The difference was attributed to sugar units in anthracyclines. In physiological pH range, the negatively charged form of THAQ weakens the overall binding ability to calf thymus DNA. Suitable chemical modifications could prevent this and lead to increase in binding constant. The molecule being much cheaper than anthracyclines could substitute them in the future.

Description: The mechanism for negative photochromism of spiropyran in silica was investigated. Prior to our study, the chemical origin of the high thermal stability of the photomerocyanine form (PMC-form) dispersed in perhydropolysilazane (PHPS), which is converted to silica at ambient temperature, had been investigated. The high thermal stability of the PMC-form is attributed to the protonated PMC-form (H⋅⋅⋅PMC-form), which is produced by intermolecular hydrogen bonding between oxide anions generated by the cleavage of the C − O bonds and the partially uncondensed Si − OH and O − H bonds of silica. Furthermore, the H⋅⋅⋅PMC-form could be thermally isomerized from the SP-form without UV light irradiation. This specific phenomenon is caused by the so-called negative photochromism. In this study, we proposed a mechanism for negative photochromism according to the relationship of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The relationship between the HOMOs was determined using cyclic voltammetry (CV) and ultraviolet photoelectron spectroscopy (UPS). On the other hand, the relationship between the LUMOs was determined from the respective optical bandgap. As a result, the HOMO level of H⋅⋅⋅PMC-form was −6.1 eV and that of SP-form was −5.3 eV. Accordingly, the thermodynamic stabilization of H⋅⋅⋅PMC-form was attributed to the thermal isomerization through negative photochromism from the SP-form. Copyright © 2011 John Wiley & Sons, Ltd. We proposed a mechanism for negative photochromism according to the relationship of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The relationship between the HOMOs was determined using cyclic voltammetry (CV) and ultraviolet photoelectron spectroscopy (UPS). The LUMOs was determined from the respective optical bandgap. The HOMO level of the H⋅⋅⋅PMC-form was −6.1 eV, and that of SP-form was −5.3 eV.

Description: Ethyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate [C 11 H 15 NO 2 S] was synthesized by the Gewald method. Its single crystals were grown from an alcohol/ethyl acetate solution at 15 °C and characterized using IR and 1 H-NMR. These single crystals were irradiated for 72 h at 298 K by a 60 Co gamma source with a dose speed of 0.864 kGy/h. After irradiation, electron spin resonance (ESR) measurements were carried out to study radiation-induced radicals in the temperature range from 120 to 450 K. Additionally, for the single crystal, ESR angular dependencies were measured in the xy , xz and yz planes of the substance. This irradiated single crystal was analyzed based on the ESR spectra. Analysis of the spectra revealed that the radical was formed by a C–H bond fission at the carbon end of the substance. It was also observed that the color of the sample changed after irradiation. The hyperfine and g parameters were determined from the experimental spectra. It was inferred from these results that the hyperfine parameters and g value exhibited anisotropic behavior. The average values of these parameters were calculated as follows: g  = 2.0088, A H1=H2  = 20.70 G, A H3=H4  = 10.80 G, A Ha  = 4.59 G, A Hb  = 3.24 G and, A N  = 6.10 G. Copyright © 2011 John Wiley & Sons, Ltd. Single crystals of ethyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate synthesized by Gewald method were irradiated for 72 h at 298K by using 60Co gamma source with dose speed of 0.864 k Gy/h. After irradiation, ESR measurements were carried out to study radiation induced radicals in the temperature range from 120 to 450K.

Description: The effect of the intramolecular H-bonding of the primary amide group on the spectral properties and reactivity of this group towards electrophiles has been studied in systematic rows of 1,2,5,6,7,8-hexahydro-7,7-dimethyl-2,5-dioxo-1-R-quinoline-3-carboxamides and 2-aryliminocoumarin-3-carboxamides using 1 H and 15 N NMR spectroscopy and the kinetics of model reactions. The upfield signal of the amide proton that is not intramolecularly H-bonded (H a ) depends on external factors such as solvent nature and concentration. At the same time, the downfield chemical shift of the H b proton (bonded by the intramolecular hydrogen bond) depends mostly on the strength of the intramolecular H-bond, which is affected by such internal factor as electron nature of substituent R. The substituent's influence on the H b proton's chemical shift is more effective in deuterochloroform medium than in DMSO- d 6 where the intramolecular hydrogen bond is less stable. The value Δδ(H) = δ(H b ) − δ(H a ) is suggested as a simple comparative spectral index of the intramolecular hydrogen bond strength in these and similar compounds. By contrast, the effect of R on the 15 N NMR chemical shift of the amide nitrogen has turned out to be too small to estimate changes of the electron density at the nitrogen. The effect of the intramolecular H-bond on the reactivity of the amide group is twofold. When the cleavage of the H-bond occurs on the rate limiting step it dramatically reduces the reaction rate. In the other case, the strengthening of the H-bond favors the reaction rate because of the increase of the electron density at the amide nitrogen. Copyright © 2011 John Wiley & Sons, Ltd. The origins of the amide proton signals nonequivalence are discussed. The value Δδ(H) = δ(H b ) − δ(H a ) is suggested as a simple comparative spectral index of the intramolecular hydrogen bond strength in these and similar compounds. The effect of the intramolecular H-bond on the reactivity of the amide group towards electrophiles is studied.

Description: The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution S N 2 mechanism to give the corresponding 2-sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ-Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4-substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4-substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted-type plot was linear with a α = −0.41 ± 0.03. The kinetic data and structure-reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k 45 versus log k 30 , the plot log( k x,3-NO2 / k H ) versus log( k x /k H ), and the Brønsted-type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd. Kinetic studies of the reaction of phenacyl bromide derivatives with sulfur nucleophiles The reaction of the substituted phenacyl bromides with thioglycolic acid and thiophenol in methanol underwent the nucleophilic substitution S N 2 mechanism. The reaction was found to proceed by a concerted mechanism. Kinetic data and structure-reactivity relationships are consistent with this concept.

Description: A series of fully-substituted 5,6-benzoquinolines covalently fused to the chlolestane framework has been synthesized to serve as model compounds for the poorly characterized components found in the heaviest fractions of petroleum, namely the asphaltenes. Acid-catalyzed cyclocondensation of an aromatic imine with 5-α-cholestan-3-one gives 5,6-benzoquinoline cycloadducts incorporating the steroidal biomarker fused to the benzoquinoline system at the 3,4-positions, with various pendent substituents in the 2-position. X-ray crystallography of three such derivatives shows that the solid-state geometries of these molecules are quite similar, and packing in the solid state appears to be dominated to a great extent by the nature of the pendent substituent. X-ray crystallography and solution phase circular dichroism spectroscopy together suggest that the conjugated benzoquinoline moiety adopts a helical conformation. Copyright © 2012 John Wiley & Sons, Ltd. 2, 3, 4-Substituted 5,6-benzoquinolines have been synthesized via the condensation reaction of an imine with 5-α-cholestan-3-one (Kozlov's procedure). With a steroid biomarker fused to the benzoquinoline core, the products serve as model compounds for components found in the heaviest fractions of petroleum (the asphaltenes). X-ray crystallography shows that packing appears dominated by the nature of the pendent substituent, while X-ray crystallography and circular dichroism spectroscopy suggest that the conjugated benzoquinoline group adopts a helical conformation.

Description: All possible types of Diels–Alder cycloadditions of 1,3- cis -butadiene to C 60 (2 in total) and to C 70 (8 in total) were theoretically investigated by the M06-2X density functional method in gas phase and solutions. An intermediate between the reactant and the transition state was located for each reaction. These intermediates except one have not been experimentally or theoretically reported before. The reactivities of the 10 reactions in both the gas phase and solutions were systematically compared based on the calculated results. The present conclusion agrees with the experimental observations and partly disagrees with the previously theoretical conclusion. Copyright © 2012 John Wiley & Sons, Ltd. All possible types of Diels-Alder (DA) cycloadditions of 1,3-cis-butadiene to C60 and C70 were theoretically investigated by the M06-2X density functional method in gas phase and solutions. An intermediate between the reactant and the transition state was located for each reaction. The present conclusion agrees with the experimental observations and partly disagrees with the previously theoretical conclusion.

Description: The combination method between asymmetric Kekulé structures (CMAK) was expanded to the structure prediction of a series of acenes and phenylenes. The structures predicted by the CMAK correspond to those calculated by the ab initio molecular orbital (MO) and B3LYP density functional methods. The CMAK can characterize the structures. The aromaticity for the whole ring and each ring in the treated compounds was estimated by the index of deviation from aromaticity (IDA). The estimated aromaticity corresponds fairly well to the characterization of the structure predicted by the CMAK. The predicted structures of linear acenes reveal the aromaticity of the central ring and also explain its reactivity. The side ring in [n]phenacene shows high aromaticity. The critical difference in the structure and aromaticity for the central six-membered ring of the isomers benzo[1,2:4,5]dicyclobutene and benzo[1,2:5,6]dicyclobutene was explained. Copyright © 2012 John Wiley & Sons, Ltd. The stable structures of polycyclic conjugated hydrocarbons were predicted by the combination method between asymmetric Kekulé structures (CMAK). The predicted structures are consistent with the aromaticity estimated by IDA. The structure prediction by CMAK explained the aromaticity and reactivity of acenes.

Description: Nanostructuring of phthalocyanine-based materials is a powerful tool towards the preparation of new materials with outstanding properties. It has been previously shown that porphyrin-functionalized and phthalocyanine-functionalized polymers give rise to nanosized aggregates. With the goal in mind of searching new phthalocyanine-containing polymeric materials that are able to self-organize into stable supramolecular nanostructures, we have prepared unsymmetrically functionalized Zn(II) phthalocyanines that are able to behave as initiators in the atom transfer radical polymerization of styrene. Hybrid phthalocyanine–polystyrene materials of different tail lengths have been prepared, and their self-organization behavior was studied by means of UV–Vis spectroscopy and transmission electron microscopy. Copyright © 2012 John Wiley & Sons, Ltd. Polymerization of styrene by ATRP using a series of Zn(II) phthalocyanine initiators proceeds in a controlled fashion and yields well-defined Zn(II)Pc-polystyrene hybrids with low polydispersities which form well-organized nanoarchitectures.

Description: A computational density functional theory study on the structural and electronic properties of several polycyclic aromatic hydrocarbon (PAH) ortho -quinones was performed and the possible mechanism of DNA-adduct formation was analyzed to evaluate its thermodynamic viability. Molecular docking techniques were applied to examine the noncovalent interactions developed when a model PAH ortho -quinone intercalates between the DNA double helix. Quantum-chemical ONIOM (our Own N-layer Integrated molecular Orbital molecular Mechanics) calculations within the structure of a DNA fragment were carried out to evaluate the significant steps of noncovalent complex and covalent adduct formation. The solvent effect was also considered by employing a continuum solvation model. The present calculations suggest that initial noncovalent interactions of the PAH o -quinone within the DNA double helix could determine the feasibility of benzo[ a ]pyrene-7,8-dione-DNA covalent adduct formation, and that dispersion-corrected functionals are more suitable for locating the noncovalent complex. Copyright © 2012 John Wiley & Sons, Ltd. Structural and electronic properties of several PAH o -quinones were studied computationally by DFT methods. The mechanism of DNA-adduct formation was also analyzed. Molecular docking and ONIOM quantum chemical calculations were performed within the structure of a DNA fragment.

Description: This research concerns the analysis of the binding properties of benzodiaza-15-crown-5 ether derivatives towards different metal ions (Mg(II), Cd(II), Ni(II), Cu(II), Zn(II), Pb(II), Hg(II) and Ag(I)) in acetonitrile and water by potentiometric and optical methods. Benzodiaza-15-crown-5 ether demonstrates high binding affinity towards Hg 2+ (lg K 11  = 12.7), whereas the stability constants of complexes with other studied cations varied from 3 to 6 logarithmic units. Copyright © 2012 John Wiley & Sons, Ltd. Detailed potentiomentic and optical analysis showed the ability of benzodiaza-15-crown-5 ether derivatives to form complexes with wide series of metal ions (Mg(II), Ca(II), Ba(II), Cd(II), Ni(II), Cu(II), Zn(II), Pb(II), Hg(II) and Ag(I)) of different structures, compositions and stability in water and acetonitrile.

Description: We studied the cleave of bis( p -nitrophenyl) phosphate (BNPP) over a pH range of 7.0–12.0 in the presence of cationic micelles of cetyldiethylethanolammonium bromide, cetyldimethylethanolammonium bromide, cetylpyridinium bromide, cetyltrimethylammonium bromide, and cetylpyridinium chloride by using different α-nucleophiles, viz acetohydroxamate, benzohydroxamate, salicylhydroxamate, butane-2,3-dione monooximate, and α-benzoin oximate ions. With the use of α-nucleophiles in cationic micellar media, the hydrolytic cleavage of BNPP was found to be approximately 10 5 -fold faster than its spontaneous hydrolysis. All reactions followed pseudo-first-order kinetics. The effect of various concentrations of cationic micelles for the reaction of BNPP and α-nucleophiles has been studied. The variation of k obs values of the reactions depends on the micellar structure, that is, head groups, hydrophobic tail length, and counter ion. Copyright © 2012 John Wiley & Sons, Ltd. Cationic micellar media accelerate the cleavage of bis( p -nitrophenyl) phosphate with α-nuleophiles than its spontaneous hydrolysis. Kinetic aspects of micellar catalysis represent a significant contribution to the observed rate in this case of hydrolysis. Surfactant-based system provides better understanding of the hydrolytic cleavage of phosphate diester.

Description: Theoretical calculations at the M05-2X/6-31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β-hydroxy ketones, 4-hydroxy-2-butanone, 4-hydroxy-2-pentanone, and 4-hydroxy-2-methyl-2-pentanone in gas phase and in m -xylene solution. The mechanism proposed is a one-step process proceeding through a six-membered cyclic transition state. A reasonable agreement between experimental and calculated activation parameters and rate constants has been obtained, the tertiary : secondary : primary alcohol rate constant ratio being calculated, at T  = 503.15 K, as 5.9:4.7:1.0 in m -xylene solution and 44.1:5.0:1.0 in the gas phase, compared with the experimental values, 3.7:1.3:1.0 and 13.5:3.2:1.0, respectively. The progress of the thermal decomposition reactions of β-hydroxy ketones has been followed by means of the Wiberg bond indices. The lengthening of the O 1 –C 2 bond with the initial migration of the H 6 atom from O 5 to O 1 can be seen as the driving force for the studied reactions. Calculated synchronicity values indicate that the mechanisms correspond to concerted and highly synchronous processes. The transition states are “advanced”, nearer to the products than to the reactants. Copyright © 2012 John Wiley & Sons, Ltd. Theoretical calculations at the M05-2X/6-31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β-hydroxy ketones in the gas phase and in m -xylene solution. The mechanism proposed is a one-step process proceeding through a six-membered cyclic transition state.

Description: We report the preparation, crystallization, and solid state characterization of a new benzannulated phenalenyl radical; a distinctive feature of this molecular solid is the absence of any well defined conducting pathway(s). In the solid state, the radicals exist as π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The magnetic susceptibility measurement indicates that, in the solid state, the radical remains paramagnetic and the fraction of Curie spins is 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σ RT  = 0.5 × 10 −6  S/cm. The conductivity value is comparable with those of similarly packed phenalenyl based neutral radicals. Copyright © 2012 John Wiley & Sons, Ltd. A stable benzannulated phenalenyl based organic neutral radical has been reported in which we identify the features that limit the conductivity of organic molecular solids. The radical exists as a π-dimer and the requisite C···C contacts between dimers are all larger than the sum of the van der Waals distances. The radical remains paramagnetic and the fraction of Curie spin available 0.55 per molecule. Pressed pellet conductivity measurements indicate a value of σ RT  = 0.5 × 10 −6  S/cm.

Description: The 13 C nuclear magnetic resonance (NMR) chemical shifts δ c of bridge group carbons (C-β, C-α, and C═N) were measured in this work for a wide set of substituted cinnamyl anilines p -XC 6 H 4 CH═CHCH═NC 6 H 4 Y- p (X = NO 2 , Cl, H, Me, MeO, or NMe 2 ; Y = NO 2 , CN, CO 2 Et, Cl, F, H, Me, MeO, or NMe 2 ) and were used to study the substituent effect. In the study on 13 C NMR chemical shifts of the titled compounds with single substituent changed, for every bridge carbon δ c , the effect of cinnamyl substituent X is opposite to that of aniline substituent Y. That is, the action of the same substituent on different aromatic rings is different from the 13 C NMR chemical shifts, and for C-β, C-α, and C═N, the choice of correlation equation depends on the ratio ρ F (Y)/ ρ R (Y). When the ratio ρ F (Y)/ ρ R (Y) is close to 1, the chemical shifts of bridge carbons can be well correlated with the single-parameter equation; otherwise, it is better to adopt the dual-parameter equation for correlation, and the further the values of ρ F (Y)/ ρ R (Y) stray from 1, the more suitable the corresponding δ c values are to be correlated with the dual-parameter equation. In the study on δ c of model compounds with simultaneous variations of substituents X and Y, for δ c (C═N), a multi-parameter correlation equation is obtained, and the substituent cross-interaction item Δ σ 2 is suitable to scale the interaction between substituents; however, for δ c (C-α and C-β), the substituent cross-interaction item Δ σ 2 is perhaps too small to be observed. The multi-parameter correlation equations can be recommended to predict well the corresponding δ c values of disubstituted cinnamyl anilines. Copyright © 2012 John Wiley & Sons, Ltd. In the study on δc values of the bridge group carbons in disubstituted cinnamyl aniline series(XPhCH=CHCH=NPhY), with a single substituent changed, the ratio ρ F (Y)/ρ R (Y) decided the choice of correlation equations, and the effect of cinnamyl substituent X is opposite to that of aniline substituent Y; With simultaneous variations of substituents X and Y, the δ c values of all bridge carbons were correlated by multi-parameter correlation equations with parameters σF and σR.

Description: The optimized minimum-energy geometries of different macrocyclic amines and their protonated structures were determined by using ab initio and density functional theory (DFT) calculations. All the gas phase optimizations and energy calculations were performed at the DFT/B3LYP/6-311++G(d,p) level of theory. The HF/6-31 + G(d,p) level was used for all single point calculations in the solution phase. Geometry optimizations indicate that the most stable structures are stabilized by intramolecular hydrogen bonds. The proton affinity (PA) of macrocyclic amines is controlled by the strength of intramolecular hydrogen bonds of macrocyclic amines. These hydrogen bonds strongly influence the basicity of heteroatoms in macrocycles. The highest PA value among the studied macrocyclic amines was found to be 264.9 kcal mol −1 for structure 7. This is comparable with PA of proton sponges such as 1,8-bis(dimethylamino)naphthalene. The solution phase calculations were carried out in the dimethyl sulfoxide solution as a commonly used solvent in organic reactions. Natural bond orbital analysis was performed to calculate the charge transfers and the second-order interaction energies ( E (2) ) between the donor and acceptor. Quantum theory of atoms in molecules (QTAIM) was also applied to determine the nature of hydrogen bonds. QTAIM studies showed that the intramolecular hydrogen bonds in these structures are electrostatic (closed-shell) interactions as well as partially covalent and partially electrostatic in nature. Copyright © 2012 John Wiley & Sons, Ltd. 1) Macrocyclic amines and their protonated structures are stabilized by intramolecular hydrogen bonds.The proton affinity values of studied macrocyclic amines are comparable to those of proton sponges such as 1,8 - bis (dimethylamino) naphthalene. The intramolecular hydrogen bonds in protonated macrocyclic amines are partially covalent and partially electrostatic in nature.

Description: The 8-oxopurine nucleosides 2′,3′,5′-tri- O -acetyl-8-oxo-7,8-dihydroguanosine (OG) and 2′,3′,5′-tri- O -acetyl-ribosyluric acid (RU) were studied for their ability to mediate the photochemical (λ 〉 300 nm) reversion of cyclobutane pyrimidine dimers to their parent pyrimidines thymine and uracil. The bimolecular reactions of these monomers proceeded at very slow rates compared with recently published work using oligonucleotide contexts; nevertheless, it was possible to make comparisons between the efficacy of OG and RU as photocatalysts as a function of pH. Although RU has a lower redox potential and anionic character, it was only equivalent to OG in facilitating thymine dimer photorepair over a broad pH range. Only OG showed pH-dependent behavior with higher activity at pH 8–9 where the base becomes deprotonated. Despite the overall low activity of OG and RU, the results are instructive with respect to a comparison of the two 8-oxopurines, and support the hypothesis that 8-oxopurine nucleosides may have played primordial roles as precursors to modern-day flavins in redox reactions of the RNA world. Copyright © 2012 John Wiley & Sons, Ltd. The 8-oxopurine nucleosides were studied for their ability to mediate the photochemical (λ 〉 300 nm) reversion of cyclobutane pyrimidine dimers to their parent pyrimidines thymine and uracil. Despite overall low activity, the results are instructive concerning the role of pH and redox potential, and support the hypothesis that 8-oxopurine nucleosides may have played primordial roles as precursors to modern-day flavins in redox reactions of the RNA world.

Description: This research extends our more recent work on the application of molecular electrostatic potential as an effective approach in describing the influence of substituent on etherification reaction rate constant of phenol derivatives. Here, in addition to electronic factor, the steric effects have also been considered for our purpose. To analyze steric effects on etherification rate constant, we use the novel energy partition scheme proposed recently by Liu [S. B. Liu, J. Chem. Phys . 2007, 126 , 244103], where the total electronic energy is decomposed into three independent components: steric, electrostatic, and fermionic quantum. In this scheme, the steric potential has also been introduced. We first derive a relationship on the basis of density functional theory to show that the etherification rate constant should be proportional to the electrostatic potential on the atomic sites. Then, a bilinear function of molecular electrostatic potential and steric energy or steric potential is proposed for estimation of etherification reaction rate constants. Taking the experimental kinetics data of 30 substituted phenols, the validity of the proposed approach has been verified in position and momentum spaces. It is worth noting that the remarkable good performance of the momentum densities, which for the first time used in calculations of steric energy for a reaction, has been observed. Finally, using the relationship between new energy partition scheme and information theory, applicability of the Shannon entropy as one of the information theoretic measures is also tested for our goal and considerable results were obtained. Copyright © 2012 John Wiley & Sons, Ltd. On the basis of a density-based quantification of the steric effect and the applicability of electrostatic potential at the nucleus, the etherification rate constants of phenol derivatives have been estimated.

Description: A novel fluorescent switchable chemosensor 1 , which is composed of an anthracene-modified calix[4]crown in the 1,3-alternate conformation, was calculated by density functional theory and time-dependent density functional theory method. Geometries, molecular orbitals and binding thermal energies were evaluated at the restricted hybrid Becke's three-parameter exchange functional using 6-31 G(d) basis set and relativistic effective core potentials. The metal–ligand and cation–π interactions were investigated acting as two main types of driving force. Our calculations clearly show that solvent effects strongly influence cation selectivity, and K + selectivity is recovered when even a few waters of hydration are considered. The calculations indicate that because of the photoinduced electron transfer effect, the addition of alkali metal ions have hardly any effect on the fluorescence of ligand 1 under neutral or basic conditions. Also, the high selectivity of ligand 1 for K + and Rb + , under acidic conditions, the complexed metal ion can result in ammonium ion deprotonation, which leads to quenching of fluorescence of 1 •H + . Copyright © 2012 John Wiley & Sons, Ltd. A novel fluorescent switchable chemosensor 1 , which is composed of a anthracene-modified calix[4]crown in the 1,3-alternate conformation, was calculated by density functional theory (DFT) and time-dependent density functional theory (TDDFT) method. The results reported here will be helpful for the future design of more sophisticated and elaborate fluorescent chemosensors for molecular recognition.

Description: The optical and resonance Raman spectra of the 2,2′: 6′,2″:6″,6-trioxytriphenyl-amine cation are measured and interpreted. This molecule contains two simultaneous types of coupling between three chromophores and two types of bridging atoms. The first and conventional coupling involves a single nitrogen bridge that couples all three aryl groups. The second is provided by the three oxygen atoms, each of which bridges two adjacent aryl groups. There are two bands in the visible region of the optical absorption spectrum; their assignment and the interpretation of the contributing orbitals and electronic states are described in terms of the neighboring orbital model that explains the effects of the two types of coupling. The bonding changes that take place in the excited electronic states are probed by resonance Raman spectroscopy intensities and analyzed using the time-dependent theory of resonance Raman spectroscopy. The optical absorption spectrum was fit using the measured vibrational frequencies and excited state distortions. The distortions correlate well with the bonding changes predicted by the neighboring orbital model. The resonance Raman data and neighboring orbital model analysis reveal that the two optical absorption bands correspond to charge transfers from aryl groups with different nodal structures in their pi orbitals. Copyright © 2012 John Wiley & Sons, Ltd. The three-chromophore cation (left) has a symmetric charge distribution in its ground state and three equivalent charge-bearing units in its lowest excited state. Coupling between the three units occurs through the central nitrogen and pair-wise through the oxygen. The effects of the coupling on the electronic and resonance Raman spectra are interpreted using the neighboring orbital model.

Description: The p K a s of 3-pyridylboronic acid and its derivatives were determined spectrophotometrically. Most of them had two p K a s assignable to the boron center and pyridine moiety. The p K a assignment performed by 11 B nuclear magnetic resonance spectroscopy revealed that both boron centers in 3-pyridylboronic acid [3-PyB(OH) 2 ] and the N -methylated derivative [3-( N -Me)Py + B(OH) 2 ] have strong acidities (p K a  = 4.4 for both). It was found that introduction of a substituent to pyridine- C atom in 3-pyridylboronic acid drastically increased the acidity of the pyridinium moiety, but decreased the acidity of the boron center, whereas the introduction to pyridine- N atom had no influence on the acidity of the boron center. Kinetic studies on the complexation reactions of 3-pyridinium boronic acid [3-HPy + B(OH) 2 ] with 4-isopropyltropolone (Hipt) carried out in strongly acidic aqueous solution indicated that the positive charge on the boronic acid influenced little on its reactivity; 3-HPy + B(OH) 2 reacts with Hipt and protonated H 2 ipt + , and its reactivity was in line with those of a series of boronic acids. Kinetics in weakly acidic aqueous solution revealed that 3-HPy + B(OH) 2 reacts with Hipt faster than its conjugate boronate [3-HPy + B(OH) 3 – ], which is consistent with our recent results. The reactivity of 3-( N -Me)Py + B(OH) 2 towards Hipt was also examined kinetically; the reactivities of 3-( N -Me)Py + B(OH) 2 and 3-( N -Me)Py + B(OH) 3 – are almost the same as those of their original 3-HPy + B(OH) 2 and 3-HPy + B(OH) 3 – , respectively. Copyright © 2012 John Wiley & Sons, Ltd. A kinetic study on the complexation reaction of cationic 3-pyridinum boronic acid [3-HPy + B(OH) 2 ] having strong acidity with 4-isopropyltropolone (HL) in solution revealed that the trigonal boronic acid has even higher reactivity than the tetragonal zwitterionic boronate ion.

Description: The synthesis of modified versions of deoxyribonucleic acid is an area that is receiving much attention. The replacement of the nitrogen atom on the nucleobases with boron atom has provided insight into deoxyribonucleic acid and ribonucleic acid stability, recognition, and replication at the atomic level. In the present research, we investigated a detailed density functional theory study of the structural, tautomeric, base-pairing ability, bond dissociation energy, and electronic properties of two boron analogues (i.e., boron substitutions at 4-position and 5-position of uracil) of uracil nucleobase. The effects of these modifications on theirs acid–base properties have been considered. Our goal is to gather data to help elucidate the structure and electronic properties of boron analogues of uracil. Density functional theory calculations were performed using a nonlocal hybrid B3LYP and 6-311++G (d,p) atomic basis set. The result of calculation revealed that the canonical ‘keto’ form is the most stable tautomeric form of uracil nucleobase and its boronated analogues in the gas phase at density functional theory and second-order Møller–Plesset levels. Hyperconjugation stabilization factors that affect the stability of generated radicals and anions in these molecules were investigated by natural bond orbital analysis. Furthermore, quantum theory of atoms in molecules analysis was performed to extract the bond critical point properties of various base pairs. The electron density can be considered as a good description of the strength of the different types of hydrogen bonding. Copyright © 2012 John Wiley & Sons, Ltd. We investigated a detailed density functional theory study of the structural, tautomeric, base-pairing ability, bond dissociation energy (BDE), and electronic properties of two boron analogues (i.e., boron substitutions at 4-position and 5-position of uracil) of uracil nucleobase and effects of these modifications on theirs acid-base properties.

Description: On the basis of the highly stable G 2 H (2 : 1) ternary complex formed by two methyl viologen cation radicals inside the cavity of cucurbit[8]uril, we prepared three monocationic 4-phenylpyridinium derivatives: 1-(hydroxyethyl)-4-phenyl-pyridinium ( 1 + ) bromide, 1-(octaethyleneglycol)-4-phenyl-pyridinium ( 2 + ) chloride, and 4-[4-(methoxymethoxy)phenyl]pyridinium ( 3 + ) iodide, as possible guests for 2 : 1 complexation inside cucurbit[8]uril. We also investigated a fourth monocationic guest ( 4 + ), in which a central vinylidene group is inserted to elongate the 4-phenyl-pyridinium residue. Using 1 H NMR and UV–Vis spectroscopic data and mass spectrometric data, we obtained unequivocal evidence for the formation of G 2 H (2 : 1) ternary complexes in all cases. The stoichiometry of the complexes was further verified by continuous variation (Job) plots, and in some cases, high resolution ESI-MS spectrometric data. Diffusion coefficient measurements, using 1 H NMR pulse gradient spin echo techniques, yielded values consistent with the formation and expected structures of the ternary complexes. Copyright © 2012 John Wiley & Sons, Ltd. A set of 4-phenyl-pyridinium derivatives were prepared and characterized as guests for the cucurbit[8]uril molecular receptor. These guests were found to form stable ternary supramolecular complexes in which two identical guests share the space inside the host cavity.

Description: The rate of thermal isomerization of ocimene in the liquid phase has been investigated in the range 90–150 °C. The rate constant for the disappearance of ocimene may be expressed by k  = 1. 3 × 10 10 e – 11994. 2/ T (min – 1 ), from which we can infer that the activation energy is 99.7 kJ mol –1 and the pre-exponential factor is 1.3 × 10 10  min –1 . The half-life for the disappearance of ocimene may be expressed by t 1/2  = 5. 2 × 10 – 11 e 11994. 2/ T (min). The conclusion has been supported by the study results that the ocimene is safe when temperature is below 100 °C. A discussion of the mechanism concerning the conversion is included. Copyright © 2011 John Wiley & Sons, Ltd. This work reports that the rate of the thermal isomerization of ocimene in the liquid phase is investigated in the range 90–150 °C. The conclusion is supported by the study results that ocimene is safe when temperature is below 100°C. Thus, not only do we design the apparatus for the preparation of ocimene by the pyrolysis of α-pinene, but also suggest that the boiling temperature of the reaction mixture of α-pinene be kept below 100 °C under vacuum.

Description: Symmetric-type carbazole derivatives show great potential for application in two-photon absorption (TPA) materials and organic light-emitting diodes. The absorption spectra and fluorescence emission spectra of three different N -alkyl symmetric-type carbazole derivatives were investigated. The density functional theory (DFT) time-dependent-DFT//Becke, three-parameter, Lee–Yang–Parr/6-31 G* method has been used to theoretically study one-photon absorption properties. The computational results are in good agreement with the available experimental values. The two-photon excited fluorescence of the compounds was surveyed by 120 fs pulse at 790 nm Ti: sapphire laser operating at 1 kHz repetition rate. Two-photon excited fluorescence was obtained in the range of 380–600 nm, and TPA cross-sections were calculated. The TPA properties of the series of compounds were investigated by the ZINDO/single and double electronic excitation configuration interaction method. The influence of the chemical structure of the compounds on two-photon optical properties was discussed. The results show how the different changes in one-photon absorption and TPA properties on the basis of lengthening the conjugated bridge and the different carbazole N -alkyl substituents are attributed to the transition dipole moment in the excited process. Copyright © 2011 John Wiley & Sons, Ltd. OPA properties of carbazole containing styrene were theoretically studied by TD-DFT. TPA properties of compounds were theoretically investigated by ZINDO/CISD method. Different carbazole N-alkyl substituents much more influence TPA of these compounds.

Description: Variation of the activation parameters in the S N 2, acyl-transfer, S N Ar, S N V, and Ad N reactions offers a uniquely useful probe for the mechanistic features of these reactions in solution. New approach uses the substituent effects on the aromatic ring to the variation of the activation parameters, Δ H ≠ and Δ S ≠ , in the above reactions in the frameworks of the Hammett-like equations in order to evaluate the resultant δ Δ H ≠ and δ Δ S ≠ reaction constants. Compensation relationships of δ Δ H ≠ versus δ Δ S ≠ allow one to estimate the contribution of changes of the internal enthalpy, δ Δ H ≠ int , to the enthalpy reaction constant, δ Δ H ≠ , that is inherent to bimolecular nucleophilic reactions and gives a single linear dependence on the Hammett ρ reaction constants for these reactions. The deviations from dependence of δ Δ H ≠ int versus ρ serve as useful points of interpretation of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the substrates, nucleophiles, and leaving groups on the mechanistic features in bimolecular nucleophilic reactions are governed by the magnitude of δ Δ H ≠ int . Copyright © 2011 John Wiley & Sons, Ltd. Δ H ≠  =  δ Δ H ≠ σ  + Δ H ≠ 0 ; δ Δ H ≠  =  δ Δ H ≠ ext  +  δ Δ H ≠ int ; δ Δ H ≠ int  = (−0.3 ± 0.2) − (6.0 ± 0.1) ρ ( r  = 0.994, s  = 1.7, n  = 82) where ρ  =  ρ ( k 1 ). The charge development in the transition state ( k 1 ) in S N 2, S N Ar, S N V, and Ad N and acyl-transfer reactions is mainly governed by the internal part of the activation enthalpy change, δ Δ H ≠ int . The deviations of the equation give a possibility to elucidate a change of TS structure or reaction mechanism.

Description: Hydroquinone combined with FeCl 3 can reduce the methanolysis time of N -vinylcarbazole in CH 3 OH from 9 h to 1 h, but the addition of hydroquinone to Fe(NO 3 ) 3 will slow the methanolysis and quench the cyclobutanation process. The addition of H 2 O 2 successfully made the FeCl 3 catalytic cyclobutanization of N -vinylcarbazole in the yield from zero up to 33%. Copyright © 2011 John Wiley & Sons, Ltd. Hydroquinone(HQ) combined with FeCl 3 can reduce the methanolysis time of N -vinylcarbazole(NVC) in CH 3 OH from 9 hours to 1 hour, the addition of H 2 O 2 successfully made the FeCl 3 catalytic cyclobutanization of NVC in the yield from zero up to 33%.

Description: The design of novel, functionalized bis-metaphenylene semiquinone (SQ) ligands and their corresponding metal complexes which combine conformational flexibility and electron-withdrawing, electron-donating, and conjugating substituents enable investigation of multiple structure–property relationships. Along these lines, we report the synthesis of three new bis(Zn II (SQ)Tp Cum,Me ) complexes containing the bis-metaphenylene coupling fragment. Using electron paramagnetic resonance spectroscopy, ab initio computations and superconducting quantum interference device magnetometry, we show how spin-density is affected by the bis-metaphenylene system substituents. Copyright © 2011 John Wiley & Sons, Ltd. We report the synthesis of three new bis(Zn II (SQ)Tp Cum,Me ) complexes containing the bis-metaphenylene coupling fragment. Using electron paramagnetic resonance, ab initio computations and superconducting quantum interference device magnetometry we show how spin-density is affected by the bis-metaphenylene system substituents.

Description: The α 1 -adrenoceptor is a target for the treatment of several conditions from hypertension to benign prostatic hyperplasia. In this paper, we describe a new analysis approach to explore the conformational space of several ligands of the α 1 -adrenoceptor and we also present the calculation of their proton affinity and basicity. For each compound a conformational search followed by a semi-empirical optimisation was performed and a selection of conformations for each ligand was subjected to further optimisation using density functional theory methods. Different positions were explored to determine the favoured site of protonation, and then, the proton affinity (in the gas phase) and basicity (using the polarisable continuum model for the aqueous solution) were calculated for each of them. In addition, an alternative method using one explicit water molecule in combination with the polarisable continuum model for aqueous solvent was explored. Moreover, the acid dissociation constant (p K a ) in water of these 26 compounds was calculated because this is an important parameter for a ligand when binding to its receptor. The experimental p K a values of six of these ligands and those of two compounds with a very low and a very large p K a were used to validate the theoretical methodology. Copyright © 2011 John Wiley & Sons, Ltd. A conformational analysis of 26 agonist/antagonist of α 1 -adrenoceptor was carried out previous to the computation at DFT level of their proton affinity, basicity (using PCM aqueous solvation) and their corresponding p K a .

Description: Carbazole derivatives have drawn increasing attention recently in organic electronic device applications because of their particular optoelectronic properties. An in-depth theoretical investigation was elaborated in this paper to reveal the molecular structures, optoelectronic properties, and the structure-property relationships of different carbazole-linked functional groups. The geometric and electronic structures in ground and the mobility for the hole and electron are both calculated by density functional theory method. The excited-state geometries of these compounds were obtained through Single-excitation Configuration Interaction method, and time-dependent density functional theory calculation results described the absorption and emission spectra properties, respectively. Some conclusions are as follows: (1) enlarging the π-conjugated area, the corresponding spectra red shifted markedly; (2) by introducing the electron-donor such as carbazole, the spectra blue shifted slightly; (3) compared with compound 1 , the spectra for these compounds are hardly influenced by introducing an electron-acceptor or heterocyclic substitution. On all accounts, these compounds are interesting optoelectronic functional materials. On the basis of their structural modifiability, the arylamine derivatives substituted carbazole compounds have great potential in the applications of organic light-emitting diodes, organic solar cells, and sensors. Copyright © 2011 John Wiley & Sons, Ltd. In different carbazole-linked functional groups, (1) enlarging the π-conjugated area, the corresponding spectra for these compounds red shifted markedly; (2) by introducing the electron-donor such as carbazole, the spectra blue shifted slightly; (3) compared with diphenylamine derivative, the spectra for these compounds are hardly influenced by introducing an electron-acceptor or heterocyclic substitution.

Description: A composite film containing photochromic spiropyran dye 1 and BaFCl:Eu was developed for X-ray dose measurement at a level of a few dozen gray (Gy). The reflectance intensity at selected wavelength, obtained from X-radiation, can be satisfactorily related to the absorbed dose in the range of 0−30 Gy. The composite film shows significant color change in the visible region, and the sensitivity of the composite to the absorbed dose was achieved based on the high molar extinction coefficient of the photomerocyanine form of dye 1. For practical application, the photoinduced blue area indicates an X-radiated area, and the initial pale pink area indicates an unexposed area. Copyright © 2011 John Wiley & Sons, Ltd. The composite film containing spiropyran dye and BaFCl:Eu exhibited a good correlation between the reflectance and adsorbed X-ray dose at a wavelength of 600 nm in the range of 0–100 Gy and exhibits an effective sensitivity range up to approximately 30Gy. The composite film also shows significant color change in the visible region. The composite film is a promising tool for a personal measurement of absorbed X-ray dose and X-ray color sensor.

Description: Bimolecular reactions of acetamide with acetamide itself, acetimidic acid and acetic acid are investigated to account for the formation of the three major experimental products from the pyrolysis of acetamide, namely ammonia, acetic acid and acetonitrile. This mechanism involves bimolecular deammonation reactions to form acetamide anhydride, acetic anhydride and N -acetyl acetamide, and the subsequent fragmentation of these intermediates into acetic acid and acetonitrile. It is found that the overall reaction barrier for the formation of the three major experimental products from the bimolecular reaction of acetamide with its enol form (acetimidic acid) amount to a 36.1 kcal/mol barrier. This barrier is in excellent agreement with the corresponding experimental data from the self-condensation of acetamide. This finding stresses on the role of acetimidic acid as a major intermediate in the pyrolysis of acetamide. The calculated activation barriers for the two available pathways in the bimolecular reaction of acetamide and acetic acid into imide and N -acetyl acetamide (36.3 kcal/mol and 24.0 kcal/mol) is in accord with the corresponding experimental activation energy of 30.1 kcal/mol for the autocatalytic reaction of acetamide with the acetic acid. Reaction rate constants are obtained for all plausible reactions. Kinetic data presented herein should be instrumental in building a robust model for the decomposition of N -alkylated amides, that is, a major structural entity in biomass. Copyright © 2011 John Wiley & Sons, Ltd. Bimolecular reactions of acetamide with acetamide itself, acetimidic acid and acetic acid are investigated to account for the formation of the three major experimental products from the pyrolysis of acetamide, namely ammonia, acetic acid and acetonitrile. Kinetic data presented herein should be instrumental in building a robust model for the decomposition of N -alkylated amides, i.e, a major structural entity in biomass.

Description: The synthesis of three new quinoxaline mono- N -oxides derivatives, namely, 2- tert -butoxycarbonyl-3-methylquinoxaline- N -oxide, 2-phenylcarbamoyl-3-ethylquinoxaline- N -oxide, and 2-carbamoyl-3-methylquinoxaline- N -oxide, from their corresponding 1,4-di- N -oxides is reported. Samples of these compounds were used for a thermochemical study, which allowed derivation of their gaseous standard molar enthalpies of formation, , from their enthalpies of formation in the condensed phase, , determined by static bomb combustion calorimetry, and from their enthalpies of sublimation, , determined by Calvet microcalorimetry. Finally, combining the for the quinoxaline- N -oxides derived in this work with literature values for the corresponding 1,4-di- N -oxides and atomic oxygen, the bond dissociation enthalpies for cleavage of the first N−O bond in the di- N -oxides, DH 1 (N–O), were obtained and compared with existing data. Copyright © 2011 John Wiley & Sons, Ltd. The first N-O bond dissociation enthalpy of three quinoxaline derivatives is obtained from the experimental gas-phase standard molar enthalpies of formation at T = 298.15 K determined for three novel N-oxide derivatives and available literature data.

Description: The aromatic character of fullerene C 40 isomers was examined by the topological resonance energy and the percentage topological resonance energy models. It was found that they all are highly aromatized at the polyvalent anionic states. The nucleus-independent chemical shifts at the cage center and the 2( N  + 1) 2 rule cannot be used as an indicator of the aromatic stabilization for C 40 isomers and their molecular ions. In addition, we utilized the bond resonance energy model to estimate the kinetic stability of C 40 isomers and their molecular ions. The results reveal that the kinetic stability of C 40 isomers can be greatly enhanced at their polyvalent anionic states. Both the aromaticity and kinetic stability are closely related to the local structure and the cyclic motion of π electrons. Copyright © 2011 John Wiley & Sons, Ltd. The aromatic character of fullerene C40 isomers was examined by the topological resonance energy and the percentage topological resonance energy models. In addition, we utilized the bond resonance energy model to estimate the kinetic stability of C40 isomers and their molecular ions. Both the aromaticity and kinetic stability are closely related to the local structure and the cyclic motion of electrons

Description: No abstract is available for this article.

Description: The antiaromatic compounds have received a great deal of attention for several decades because of their unusual electronic structures. The electronic structures and properties of antiaromatic pentalene and its six nitrogen heterocyclic derivatives were systematically studied by the density functional theory at the Becke, three-parameter, Lee–Yang–Parr level with 6-31G* basis set. The results indicated that all the monomers have stable singlet states and remarkable bond-length alternations. From the dimer to polymer in those molecules, pentalene(P), cyclopenta[ b ]pyrrole(CPP), cyclopenta[ d ]imidazole(CPI), pyrrolo[2,3- b ]pyrrole(PP1) and pyrrolo[3,2- d ]imidazole(PI) are stable diradical structures; pyrrolo[3,2- b ]pyrrole (PP2) and imidazo[4,5- d ]imidazole(II) are stable singlet ground states. The electronic properties including bond length, bond-length alternation, electron density at bond critical points, Wiberg bond index and nucleus-independent chemical shift were analyzed. It was found that in diradical molecules the bond-length alternations are diminished, the charge tends to equilibrate, the π-electron delocalization and conjugation are strengthened. The electronic properties of singlet ground state molecules have nearly no variations from monomers to polymers. The band structure analysis shows that diradical structure molecules have small band gaps (〈1.0 eV), wide bandwidth and small effective masses of holes and electrons which suggest that diradical structure molecules are very good candidates for conductive materials. Copyright © 2011 John Wiley & Sons, Ltd. The electronic structures of anti-aromatic pentalene and its nitrogen-containing heterocyclic analogs were computed DFT at the B3LYP/6-31G(d) level of theory. All monomers were singlet ground states, their respective dimers, trimers, and polymers are triplet ground states (with the exception of PP2 and II). The aromaticity/antiaromaticity and band structures of these molecules were analyzed. It predicted that polymers of CPP and CI with small band gaps could be potential conductors.

Description: The addition of free radicals and the 1,3 dipolar cycloaddition onto pristine and lithium-doped C 60 were studied by means of the Perdew–Burke–Ernzerhof (PBE) and M06-2X density functionals. In all cases, lithium increased the reactivity even though for the 1,3 dipolar cycloaddition onto C 60 the change observed with respect to bare C 60 was minimal. Both functionals employed gave similar encapsulation energies for Li@C 60 namely, 33.1 and 38.2 kcal/mol at the PBE/6-31G* and M06-2X/6-31G*, respectively. However, the increased reactivity because of lithium doping determined at the PBE level is smaller as compared with that computed with the M06-2X functional, whereas that determined at the second-order Møller–Plesset (MP2) level is the largest one. For example, using the M06-2X functional the binding energy of fluorine to Li@C 60 is 28.5 kcal/mol larger than that determined for C 60 , whereas at the PBE/6-31G* level it is predicted to be increased by 24.7 kcal/mol. The results clearly suggest that Li@C 60 is a much better free radical scavenger than C 60 . Finally, the complex hindered rotations of lithium inside C 60 are expected to be strongly inhibited because lithium doping increases the well depth between the cage center and the equilibrium position near the addition site of the lithium atom. Copyright © 2011 John Wiley & Sons, Ltd. Lithium doping significantly increases the free radical addition energies to fullerenes.

Description: In this paper, 72 samples of disubstituted benzylideneanilines were all synthesized, and their UV data were measured in anhydrous ethanol. In the study on the UV energy of the titled compounds with single substituent changed, for the effect of the aniline substituent Y on the UV wavenumbers, its UV data can be correlated with a dual-parameter equation; for the effect of benzylidene substituent X on the UV data, its UV energy can be correlated with a single-parameter equation (Y is an electron-withdrawing group and H) or a dual-parameter equation (Y is an electron-donating group). In the study on the UV energy of model compounds with double substituents changed, a correlation equation between the UV absorption wavenumbers and substituent constants and σ p , was obtained. For 72 samples of 4,4′-disubstituted benzylideneanilines, the correlation coefficient was 0.9876, and the standard deviation s was only 358.46 cm –1 . The equation can be used to predict well the UV energy of BA derivatives. It was found that Δσ 2 is a better parameter than σ XY to scale the substituent cross-interaction effect on the UV wavenumbers of benzylideneanilines molecules. The results implied that the law of substituent effect on the UV energy of titled compounds is different from that of substituted stilbenes, and it is helpful to understand the effect of substituent effects on the chemical and physical properties of conjugated compounds with an imine bridging group (C = N) or a nonplanar parent. Copyright © 2011 John Wiley & Sons, Ltd. For 4, 4′-disubstituted benzylideneanilines with an imine bridging group (C = N), the substituent effect on their UV energy is different from that on UV energy of substituent stilbenes with a bridge group (C = C). It is not only related to the σ CC ex , but also associated with the σ p . And it was found that the Δσ 2 is a better parameter than the σ XY to scale the substituent cross-interaction effect on the UV wavenumbers of XBAY molecules.

Description: Theoretical calculations at the M05-2X/6-31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β-hydroxy ketones, 4-hydroxy-2-butanone, 4-hydroxy-2-pentanone, and 4-hydroxy-2-methyl-2-pentanone in gas phase and in m -xylene solution. The mechanism proposed is a one-step process proceeding through a six-membered cyclic transition state. A reasonable agreement between experimental and calculated activation parameters and rate constants has been obtained, the tertiary : secondary : primary alcohol rate constant ratio being calculated, at T  = 503.15 K, as 5.9:4.7:1.0 in m -xylene solution and 44.1:5.0:1.0 in the gas phase, compared with the experimental values, 3.7:1.3:1.0 and 13.5:3.2:1.0, respectively. The progress of the thermal decomposition reactions of β-hydroxy ketones has been followed by means of the Wiberg bond indices. The lengthening of the O 1 –C 2 bond with the initial migration of the H 6 atom from O 5 to O 1 can be seen as the driving force for the studied reactions. Calculated synchronicity values indicate that the mechanisms correspond to concerted and highly synchronous processes. The transition states are “advanced”, nearer to the products than to the reactants. Copyright © 2012 John Wiley & Sons, Ltd. Theoretical calculations at the M05-2X/6-31+G(d) level of theory have been carried out in order to explore the nature of the mechanism of the thermal decomposition reactions of the β-hydroxy ketones in the gas phase and in m -xylene solution. The mechanism proposed is a one-step process proceeding through a six-membered cyclic transition state.

Description: Recent interest in the self-healing ability of the laser dye 1-amino-2-methylanthraquinone, Disperse Orange 11, has lead us to investigate the possible alternative mechanisms of action, either intramolecular proton transfer (PT) or twisted intramolecular charge transfer (TICT) formation. AMPAC semiempirical PM3 CI (all single excited configurations) potential energy surfaces searches have been conducted with either reaction mechanism. Based purely on the potential energy surface results, no state, S0, T1, or S1, seems especially likely to be kinetically favorable for PT. The T1 state is favorable thermodynamically for PT. However, the S1 state TICT reaction is both thermodynamically favorable and kinetically preferred over all PT reactions. There is also a favorable T1 TICT reaction, but much slower kinetically on the triplet surface than S1 TICT. The Wentzel–Kramers–Brillouin (WKB) method has been used to ascertain proton tunneling contributions to PT. Even with proton tunneling, S1 TICT is still more highly favored, though proton tunneling could make the T1 PT reaction competitive depending on the rate of intersystem crossing. We also examine spectroscopic properties of PT transfer and TICT reaction path entities in comparison with published experimental evidence. However, this comparison leads to ambiguous findings that suggest that electronic spectral properties alone will not fully clarify the mechanism. Overall, results suggest that the TICT mechanism is the most likely for optical damage and self-repair for Disperse Orange 11, and might be considered for the damage and repair mechanisms for other organic solid state laser materials. Copyright © 2012 John Wiley & Sons, Ltd. Twisted intramolecular charge transfer transitions (TICT) have been identified as the possible mechanism behind optical damage and self-repair for the Disperse Orange laser dye. Semiempirical PM3 calculations of the potential energy surface and WKB approximation proton tunneling calculations suggest S1 state intramolecular proton transfer (PT) is less likely. It is possible that intersystem crossing could lead to a reasonably competitive T1 PT reaction. Shown is the TICT state charge distribution.

Description: A kinetic study was carried out for the reaction of benzaldehyde and borane (BH 3 ) in tetrahydrofuran. The effect of BH 3 concentration on the rate constant showed that the reaction order with respect to BH 3 was 1.6. Substituent effects gave a linear Hammett plot with a ρ value of −0.51. It was concluded that the reaction proceeds through a rate-determining hydride-transfer transition state with two BH 3 molecules, in which one molecule of BH 3 acts as a reducing agent and the other serves as a catalyst. Copyright © 2011 John Wiley & Sons, Ltd. Kinetic study for the reaction of benzaldehyde and BH 3 in THF showed that the reaction order with respect to BH 3 was 1.6. Substituent effects gave a linear Hammett plot with a ρ value of −0.51. It was concluded that the reaction proceeds through a rate-determining hydride-transfer TS, in which one molecule of BH 3 act as reducing agent and the second BH 3 molecules serves as catalyst.

Description: The intramolecular complexes containing coordination bonds Si←N or Si←O are distinguished for their stereochemical nonrigidity resulting in interconversion between isomers, that is, ligand-site exchange. The influence of the substituents bound to the silicon atom on the free energies of activation for ligand exchange Δ G ≠ of specific interest is poorly understood. In this work, the literature data on substituent influence on the energies Δ G ≠ for 13 series of the complexes have been considered, using the correlation analysis. On the basis of the obedience of the energies Δ G ≠ to the linear free energy relationship, it has been established for the first time that the Δ G ≠ values depend not only on the inductive and resonance effects but also on the polarizability and steric effects of substituents. The reason for the occurrence of the polarizability effect is the appearance of excess charges on Si and N (or O) atoms as a result of intramolecular coordination consisting in the charge transfer from the donor center (N or O atom) to the acceptor one (Si atom). In some series the contribution of the polarizability or steric effect to the overall change in Δ G ≠ because of the influence of substituents is a maximum. An understanding of these effects may give a better insight into the mechanism of nucleophilic substitution, involving organoelement compounds. Copyright © 2012 John Wiley & Sons, Ltd. The free energies of activation for ligand exchange Δ G ≠ values depend not only on the inductive and resonance effects but also on the polarizability and steric effects of substituents.

Description: The base-promoted solvolysis of a series of O , O -dimethyl O -aryl and O , O -dimethyl O -alkyl phosphorothioates (1) as well as O , O -dimethyl O -aryl and O , O -dimethyl O -alkyl phosphates (2) was studied computationally by density functional theory methods in methanol and water continuum media to determine the transition between concerted and stepwise processes. In addition, an experimental study was undertaken on the solvolysis of these series in basic methanol and water. The computations indicate that the solvolytic mechanism for series 1 involves lyoxide attack anti to the leaving group in a concerted manner with good leaving groups having p K a Lg values 〈 12.3 in methanol and in a stepwise fashion with the formation of a 5-coordinate thiophosphorane intermediate when the p K a Lg  〉 12.3. A similar transition from concerted to stepwise mechanism occurs with series 2 in methanol as well as with series 1 and 2 in water, although for the aqueous solvolyses with hydroxide nucleophile, the transitions between concerted and stepwise mechanisms occur with better leaving groups than in the case in methanol. The computational data allow the construction of Brønsted plots of log k 2 −OS versus p K a Lg in methanol and water, which are compared with the experimental Brønsted plots determined with these series previously and with new data determined in this work. Both the computational and experimental Brønsted data reveal discontinuities in the plots between substrates bearing O -aryl and O -alkyl leaving groups, with the gradients of the plots being far steeper than, and non-collinear with, the O -aryl leaving groups for solvolysis of the O -alkyl-containing substrates. These discontinuities signify that care should be exercised in interpreting breaks in Brønsted plots in terms of changes in rate-limiting steps that signify the formation of an intermediate during a solvolytic process. Copyright © 2011 John Wiley & Sons, Ltd. DFT computations and experimentation shows that the base-promoted cleavage of phosphates and phosphorothioate triesters follows and enforced concerted pathway with good aryloxy leaving groups, and a stepwise pathway with poor leaving groups. Brønsted plots of log k 2 -OS vs. pK a lg indicate that there is a discontinuity between the linear plots for aryloxy and alkoxy leaving groups that stems not from a change in rate limiting step, but from the different electronic nature of the two sets of leaving groups.

Description: Ab initio and semi-empirical calculations were performed on the monomers, dimers and tetramers of the antidiabetic drug nateglinide to understand the conformational preferences and to explore their possible relation with polymorphism. The reported crystal structure of bis(nateglinide) hydronium chloride shows one asymmetric unit consisting of four different conformations of the drug nateglinide. The Becke, three-parameter, Lee–Yang–Parr /6-31+G(d,p) optimizations indicate that these conformers are energetically quite comparable and the differences disappear in gas phase. Our analysis shows that Φ (phi) torsion angle of this phenylalanine derivative is responsible for the observed differences in stability among the nateglinide conformations. Four different polymorphs of nateglinide (B, H, S and X2) were reported but the structural differences are not available. This quantum chemical study on the dimers of nateglinide helps in proposing the structures of polymorphs. As per the quantum chemical analysis, the dimer N-44 is the structure of the stable polymorph, whereas, the dimers N-AA, N-CC and N-AC are almost isoenergetic, thus proposed to be the structures of metastable state. The dimerization and tetramerization energies are estimated to be about −9.0 and −38.67 kcal/mol, respectively. The extra stability in tetrameric state compared with the dimeric form is attributed to additional hydrophobic and van der Waals interactions. Copyright © 2011 John Wiley & Sons, Ltd. The antidiabetic drug nateglinide exhibits conformational polymorphism. Quantum chemical analysis shows that Φ (phi) torsion angle of this phenylalanine derivative is responsible for the observed differences in stability among the nateglinide conformations ( N-A , N-C and N-4 ). Ab initio studies indicate that dimer N-44 is the structure of the stable polymorph, whereas, dimers N-AA , N-CC and N-AC are proposed as structures of the metastable state.

Description: The cycloaddition between glyoxylate imines possessing two chiral auxiliaries, N -( R )- or N -( S )-1-phenylethyl and 8-phenylmenthyl or 8-phenyl neo menthyl, and cyclopentadiene is described. Computational calculations using density functional theory with the Becke, three-parameter, Lee–Yang–Parr functional and the 6-31G(d) basis set were performed to better understand the highly diastereoselective mechanism and the exo -selectivity observed experimentally for these ionic aza-Diels–Alder reactions. Copyright © 2011 John Wiley & Sons, Ltd. The cycloaddition between glyoxylate imines possessing two chiral auxiliaries, N -( R )- or N -( S )-1-phenylethyl and 8-phenylmenthyl or 8-phenyl neo menthyl, and cyclopentadiene is described. Computational calculations using density functional theory with the Becke, three-parameter, Lee–Yang–Parr functional and the 6-31G(d) basis set were performed to better understand the highly diastereoselective mechanism and the exo -selectivity observed experimentally for these ionic aza-Diels–Alder reactions.

Description: Cope rearrangement mechanisms and the homoaromaticity of semibullvalene, barbaralane, and 1,5-methanosemibullvalene in the ground and lowest excited states were studied by ab initio methods. In the ground state, the rearrangement reactions of semibullvalene and barbaralane occurred concertedly through the transition states with C 2v symmetry, and the transition states had a homoaromatic nature. In particular, the transition state of barbaralane exhibited the strongest homoaromaticity among the three systems treated here. On the other hand, for 7,8-methanosemibullvalene, the structure with C 2v symmetry was not a transition state but one with a stable energy minimum. The energy minimum structure with C 2v symmetry had a biradical character. The lowest excited states of semibullvalene and barbaralane were the excitation to the σ* anti-orbital, 1 B 2 and 1 B 1 states, and led to near di-allyl states. The lowest excitation state of 1,5-methanosemibullvalene had C s symmetry and was the A″ state excitation in one side of two allyl parts. Copyright © 2011 John Wiley & Sons, Ltd. Cope rearrangement mechanisms of semibullvalene, barbaralane, and 1,5-methanosemibullvalene in the ground and lowest excited staes were studied by the CiLC analysis on the basis of ab initio MO methods. The homoaromaticity of these compounds were also evaluated by the index of deviation fromaromaticity (IDA). The mechanisms and aromaticity for 1,5-methanosemibullvalene showed very different behavior from those for other compounds.

Description: Cleavage of disulfide bonds is a common method used in linking peptides to proteins in biochemical reactions. The structures, internal rotor potentials, bond energies, and thermochemical properties (Δ f H °, S°, and Cp( T )) of the S–S bridge molecules CH 3 SSOH and CH 3 SS(=O)H and the radicals CH 3 SS•=O and C•H 2 SSOH that correspond to H-atom loss are determined by computational chemistry. Structure and thermochemical parameters (S° and Cp( T )) are determined using density functional Becke, three-parameter, Lee–Yang–Parr (B3LYP)/6-31++G (d, p), B3LYP/6-311++G (3df, 2p). The enthalpies of formation for stable species are calculated using the total energies at B3LYP/6-31++G (d, p), B3LYP/6-311++G (3df, 2p), and the higher level composite CBS–QB3 levels with work reactions that are close to isodesmic in most cases. The enthalpies of formation for CH 3 SSOH, CH 3 SS(=O)H are −38.3 and −16.6 kcal mol −1 , respectively, where the difference is in enthalpy RSO–H versus RS(=O)–H bonding. The C–H bond energy of CH 3 SSOH is 99.2 kcal mol −1 , and the O–H bond energy is weaker at 76.9 kcal mol −1 . Cleavage of the weak O–H bond in CH 3 SSOH results in an electron rearrangement upon loss of the CH 3 SSO–H hydrogen atom; the radical rearranges to form the more stable CH 3 SS· = O radical structure. Cleavage of the C–H bond in CH 3 SS(=O)H results in an unstable [CH 2 SS(=O)H]* intermediate, which decomposes exothermically to lower energy CH 2  = S + HSO. The CH 3 SS(=O)–H bond energy is quite weak at 54.8 kcal mol −1 with the H–C bond estimated at between 91 and 98 kcal mol −1 . Disulfide bond energies for CH 3 S–SOH and CH3S–S(=O)H are low: 67.1 and 39.2 kcal mol −1 . Copyright © 2011 John Wiley & Sons, Ltd. Structures, internal rotor potentials, thermochemical properties (δfH o , S o and Cp(T)) and bond energies on the S-S bridge molecules CH 3 SSOH and CH 3 SS(=O)H and radicals CH 3 SS•=O and C•H 2 SSOH are determined using DFT and CBS-QB3 computational chemistry methods. Disulfide bond energies for CH3S–SOH and CH3S–S(=O)H are 67.1 and 39.2 kcal mol−1. The CH3SS(=O)−H bond energy is only 54.8 kcal mol−1. The C−H bond energy of CH 3 SSOH is 99.2 and the O−H bond energy is 76.9 kcal mol−1

Description: Synthesis yields of organic reactions are one of the most important factors in ranking synthesis routes created by synthesis route design systems such as Transform-Oriented Synthesis Planning and Knowledge base-Oriented Synthesis Planning. If it is possible to predict the yields of synthesis reactions before starting experiments, one can easily determine an order of synthesis routes for experimental works. In the present study, the reaction profiles of the Curtius rearrangement with different substituents were calculated to generate an equation predicting experimental yields of this reaction. Reactions followed by the formation of isocyanates were also analyzed to consider the relationship between reaction times and experimental yields. A partial least squares (PLS) regression was used to correlate the experimental yields with the calculated activation energies, E a ( calc ), together with experimental conditions such as dielectric constants of solvents, reaction times, and reaction temperatures as explanatory variables. Although the PLS regression using all the data gave very poor results, we succeeded in making a model equation with R 2  = 0.887 using a modified data set. However, there is a conflict between the predictability and the interpretability on the reaction time. This discrepancy mainly comes from unnecessarily long reaction times in the experiments for azides with calculated E a values of less than 33 kcal mol –1 . To construct a good model equation for the experimental yields of the Curtius reaction, we have to use data sets obtained from within 90 min of the reaction for the PLS regression. Copyright © 2011 John Wiley & Sons, Ltd. We tried to predict the yields observed for the Curtius rearrangement using the Ea ( calc ) values from DFT calculations, together with the reaction conditions. In order to construct a good model equation for the experimental yields of the Curtius reaction, we have to use those obtained from the reaction within 90 min for the PLS regression.