ALBERT

Description: Kinetics and equilibrium of the acid-catalyzed disproportionation of cyclic nitroxyl radicals R 2 NO • to oxoammonium cations R 2 NO + and hydroxylamines R 2 NOH is defined by redox and acid–base properties of these compounds. In a recent work ( J. Phys. Org. Chem . 2014, 27, 114-120), we showed that the kinetic stability of R 2 NO • in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R 2 NO + and R 2 NOH to R 2 NO • and found that increasing in – I -effects of substituents greatly reduces the overall equilibrium constant of the reaction K 4 . This occurs because of both the increase of acidity constants of hydroxyammonium cations K 3H+ and the difference between the reduction potentials of oxoammonium cations E R2NO+/R2NO• and nitroxyl radicals E R2NO•/R2NOH . pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E 1/3Σ and bond dissociation energies D(O–H) for hydroxylamines R 2 NOH in water were determined. For a wide variety of piperidine- and pyrrolidine-1-oxyls values of p K 3H+ and E R2NO+/R2NO• correlate with each other, as well as with the equilibrium constants K 4 and the inductive substituent constants σ I . The correlations obtained allow prediction of the acid–base and redox characteristics of redox triads R 2 NO • –R 2 NO + –R 2 NOH. Copyright © 2014 John Wiley & Sons, Ltd. The overall equilibrium constant K 4 of disproportionation of nitroxyl radicals 1 depend on the difference of their pH-dependent reduction potentials to hydroxyammonium cations 3 H + and reduction potentials of oxoammonium cations 2 to 1 : E 1 / 3 Σ  −  E 2 / 1  = ( RT / F )ln K 4 . – I -Effects of substituents R and heterocycle contraction increase the rate constant of comproportionation k − 2 , acidity constants of protonated nitroxyl radicals K 1 H+ and hydroxylamines K 3 H+ , thus reducing the constant K 4  =  k 2  /  (k − 2  ×  K 1 H+  ×  K 3 H+ ) in the studied series of compounds a–i by more than seven orders of magnitude.

Description: The ―NH 2 , ―NO 2 , ―NHNO 2 , ―C(NO 2 ) 3 and ―CF(NO 2 ) 2 substitution derivatives of 4,4′,5,5′-tetranitro-2,2′-1H,1′H-2,2′-biimidazole were studied at B3LYP/aug-cc-pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics (MM) methods. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. The thermal stability of the title compounds was investigated via the energy gaps ( ∆E LUMO − HOMO ) predicted. Results show that molecules T5 ( D  = 10.85 km·s −1 , P  = 57.94 GPa) and T6 ( D  = 9.22 km·s −1 , P  = 39.21 GPa) with zero or positive oxygen balance are excellent candidates for high energy density oxidizers (HEDOs). All of them appear to be potential explosives compared with the famous ones, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocane (HMX, D  = 8.96 km·s −1 , P  = 35.96 GPa) and hexanitrohexaazaisowurtzitane (CL-20, D  = 9.38 km·s −1 , P  = 42.00 GPa). In addition, bond dissociation energy calculation indicates that T5 and T6 are also the most thermally stable ones among the title compounds. Copyright © 2014 John Wiley & Sons, Ltd. The ―NH 2 , ―NO 2 , ―NHNO 2 , ―C(NO 2 ) 3 and ―CF(NO 2 ) 2 substitution derivatives of 4,4',5,5'-tetranitro-2,2'-1H,1'H- 2,2'-biimidazole were studied at B3LYP/aug-cc- pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics methods. The thermal stability of the title compounds was investigated via the energy gaps (ΔELUMO-HOMO) predicted. Results show that 4,4',5,5'-tetranitro-2,2'- 1H,1'H- 2,2'-biimidazole-1,1'-ditrinitromethyl amino (T5), (D = 10.85 km s –1 , P = 57.94 GPa) and 4,4',5,5'-tetranitro-2,2'-1H,1'H-2,2'- biimidazole-1,1'-difluorodinitromethylamino (T6) (D = 9.22 km s –1 , P = 39.21 GPa) with zero or positive oxygen balance, are excellent candidates for high energy density oxidizers.

Description: Previous studies of the C(3)-hydrogen/deuterium exchange reactions of the triazolium ion conjugate acids of triazolyl N-heterocyclic carbenes revealed a change of mechanism under acidic conditions with N1-protonation to a dicationic salt. Interestingly, the data suggested an increase in p K a N1 in the presence of a N -pentafluorophenyl substituent relative to other N -aryl substituents with hydrogens or methyl substituents rather than fluorines at the ortho -positions. To probe the presence of an apparent donor effect of a N -pentafluorophenyl substituent, which differs from the more common electron withdrawing effect of this group, we have studied the analogous deuterium exchange reactions of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N -aryl ring. These include triazolium salts with N -2,4,6-tribromophenyl , N -2,6-dichlorophenyl , N -2-pyridyl and N -2-pyrimidinyl substituents. The log k ex – p D profiles for , and were found to show similar trends at lower p D s as for the previously studied N -pentafluorophenyl triazolium salt, hence supporting the presence an apparent donor effect on p K a N1 . Surprisingly, the log k ex – p D profile for N -pyridyl salt uniquely showed acid catalysis at lower p D s. We propose herein that this data is best explained by invoking an intramolecular general base role for the N -(2-pyridyl) substituent in conjunction with N1-protonation on the triazolium ring. Finally, the second order rate constants for deuteroxide ion catalysed C(3)-H/D exchange ( k DO , M −1  s −1 ), which could be obtained from data at p D s 〉1.5, were used to provide estimates of C(3)-carbon acid p K a C3 values for the four triazolium salts . Copyright © 2014 John Wiley & Sons, Ltd. We have studied the C(3)-H/D exchange reactions in D 2 O of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N -aryl ring. The log k ex – p D rate profiles in each case are consistent with a change in mechanism at p D 〈 1.5 as a result of N 1-deuteronation of the triazole ring. In addition, formal acid catalysis of deuterium exchange was uniquely observed for the N -pyridyltriazolium salt providing evidence for a possible intramolecular proton transfer reaction involving the pyridyl substituent.

Description: The kinetics of the gas-phase thermal decomposition of the α-ketoester methyl benzoylformate was carried out in a static system with reaction vessel deactivated with allyl bromide, and in the presence of the free radical inhibitor propene. The rate coefficients were determined over the temperature range of 440–481 °C and pressures from 32 to 80 Torr. The reaction was found to be homogenous, unimolecular and obey a first-order rate law. The products are methyl benzoate and CO. The temperature dependence of the rate coefficient gives the following Arrhenius parameters: log 10 k (s −1 ) = 13.56 ± 0.31 and E a (kJ mol −1 ) = 232.6 ± 4.4. Theoretical calculations of the kinetic and thermodynamic parameters are in good agreement with the experimental values using PBE1PBE/6-311++g(d,p). A theoretical Arrhenius plot was constructed at this level of theory, and the good agreement with the experimental Arrhenius plot suggests that this model of transition state may describe reasonably the elimination process. These results suggest a concerted non-synchronous semi-polar three-membered cyclic transition state type of mechanism. The most advanced coordinate is the bond breaking C δ+ --- δ- OCH 3 with an evolution of 66.7%, implying this as the limiting factor of the elimination process. Copyright © 2014 John Wiley & Sons, Ltd. Kinetic of the gas-phase thermal decomposition of methyl benzoylformate was carried at 440–481 °C and 32–80 Torr. The product formation suggests both experimentally and theoretically a three-membered cyclic transition state mechanism.

Description: Interstellar chemical reactivity forms complex organic molecules implying different intermediates. In this mini review, reactions arising in/on interstellar ices are presented. These ices are a place where molecules are formed and where they can evolve under thermal and nonthermal effects. We present in this paper different intermediates that have been detected in experimental simulations of interstellar ices. Ionic, neutral, and radical intermediates have been characterized by different means allowing the building of an ice chemical network explaining their formation. Copyright © 2014 John Wiley & Sons, Ltd. Jean-Baptiste Bossa studied Chemistry at Aix-Marseille University in France. He received his PhD in Chemistry from Aix-Marseille University in 2010 under the supervision of Prof Thierry Chiavassa. He is currently the principal investigator of a research project founded by the Marie Skłodowska-Curie actions and conducted at both Leiden University (the Netherlands) and the University of Cologne (Germany). His research interests are in the field of laboratory astrophysics.

Description: Bicyclo[3.1.1]heptâ2âene was first prepared and well identified in 1972. In 1974, the degenerate thermal isomerization involving 1â d â and 3â d âbicyclo[3.1.1]heptâ2âene was approached successfully, as one of the two deuteriumâlabeled structures was selected, heated, and equilibrated. There has been no further study of this degenerate isomerization. Here, a detailed outline of reaction trajectories for d 2 âlabeled bicyclo[3.1.1]heptâ2âenes is given that will establish the four independent kinetic parameters needed for 20 linking paths between six d 2 âspecies. The use of racemates, eliminating chiral separations and dissections, provides degenerate isomerization paths providing this method with general utility. Copyright © 2014 John Wiley & Sons, Ltd. The use of racemic doubly deuteriumâlabeled species can be used to obtain, for the first time, the full set of four unique rate constants for the degenerate rearrangements of d 2 âbicyclo[3.1.1]heptâ2âene. The expectations for deuterium isotope 1 Î effects on 13C NMR chemical shifts are tabulated and show that it can be used to quantify the isotopomers and monitor the reactions as they progress.

Description: Oligoâ p âphenylene ethynylenes have been shown to be useful for their sensing and biocidal capabilities. In this study, we examine the influence of interfacial water on the photophysical properties of a carboxyesterâsubstituted compound in this class through analysis of the aggregation with ionic surfactants, solvent isotope effects, and classical molecular dynamics simulations. The results of this study reveal that the presence of carboxyester groups leads to highly structured interfacial water and results in quenched fluorescence. In addition, the results indicate that hydrogen bonding is essential for aggregate formation. Copyright © 2014 John Wiley & Sons, Ltd. The influence of Hâbonding with aqueous solvent on the fluorescence of an oligoâpâphenylene ethynylene was explored using a combined experimental and computational approach. Fluorescence spectra and lifetimes were compared in deuterium oxide and water, and complexation with an ionic surfactant revealed striking changes in fluorescence and absorbance spectra. Classical molecular dynamics studies revealed and extended Hâbonding networks are involved in surfactant complexation. The results of this study reveal the importance of the carboxyester moiety and Hâbonding in fluorescent sensors.

Description: The values of the enthalpy (53.3; 51.3; 20.0âkJ mol â’1 ), entropy (â’106; â’122; â’144âJ mol â’1 K â’1 ), and volume of activation (â’29.1; â’31.0; â’cm 3 mol â’1 ), the reaction volume (â’25.0; â’26.6; â’cm 3 mol â’1 ) and reaction enthalpy (â’155.9; â’158.2; â’150.2âkJ mol â’1 ) have been obtained for the first time for the ene reactions of 4âphenylâ1,2,4âtriazolineâ3,5âdione , with cyclohexene , 1âhexene , and with 2,3âdimethylâ2âbutene , respectively. The ratio of the values of the activation volume to the reaction volume (â V â  corr /Î V r ââ’â n ) in the ene reactions under study, â+â â’ and â+â â’ , appeared to be the same, namely 1.16. The large negative values of the entropy and the volume of activation of studied reactions â+â â’ and â+â â’ better correspond to the cyclic structure of the activated complex at the stage determining the reaction rate. The equilibrium constants of these ene reactions can be estimated as exceeding 10 18 L mol â’1 , and these reactions can be considered irreversible. Copyright © 2014 John Wiley & Sons, Ltd. The values of â H â  , â S â  , â V â  , â H r ââ’â n and â V r ââ’â n of the ene 1â+â4â’5 , 1â+â6â’7 and 1â+â8â’9 reactions have been determined and compared with those of the DielsâAlder reactions.

Description: A polymer (PAIM) containing the functional groups imidazole and carboxylic acid acts as a nanoreactor to accelerate deacylation and dephosphorylation reactions. The synthesis was designed to position the two functional groups next to each other, allowing cooperativity. The catalytic efficiency of the polymer was evaluated for the hydrolytic cleavage of pânitrophenyl acetate (PNPA) and diethyl 2,4âdinitrophenyl phosphate (DEDNPP). PAIM was both efficient and promiscuous, increasing the rates of all reactions up to 10 7 âfold. Copyright © 2014 John Wiley & Sons, Ltd. A polymer containing the functional groups imidazole and carboxylic acid acts as a nanoreactor to accelerate deacylation and dephosphorylation reactions up to 10 7 âfold.

Description: The mechanism of palladiumâcatalyzed bicyclization of 2âalkynylhalobenzenes and propargylic alcohols for the formation of indeno[1,2]furans has been studied computationally with the aid of density functional theory (DFT). Full free energy profiles are computed for different reaction equations between different reaction substrates. The calculation results showed that the catalytic cycle is found to contain six steps, oxidative addition, ligand substitution, first Cââ¡âC triple bond insertion, rearrangement, second Cââ¡âC triple bond insertion and reductive elimination, with the reductive elimination being the rateâdetermining step for the different reaction equations (1), (2) and (3). Our calculations are consistent with experimental observations. Copyright © 2014 John Wiley & Sons, Ltd. The mechanism of palladiumâcatalyzed bicyclization of 2âalkynylhalobenzenes and propargylic alcohols for the formation of indeno[1,2]furans has been investigated via DFT calculations. The results showed that the catalytic cycle is found to contain six steps, oxidative addition, ligand substitution, first Cââ¡âC triple bond insertion, rearrangement, second Cââ¡âC triple bond insertion and reductive elimination, with the reductive elimination being the rateâdetermining step for the different reaction equations (1) , (2) and (3) , respectively.

Description: The energetics of nucleophilic addition of pyridine to polyenes of various lengths and the corresponding protonation of these polyenes by methyl ammonium fluoride was computationally determined using ab initio methods. These reactions were also studied in the presence of an electric field (2.5 and 5âMV/cm) oriented along the polyene long axis in the direction which will enhance the reaction. Assuming linearity over a long range, and extrapolating the data for 2.5âMV/cm to 10ânm chain length gave a reduction in the activation energy of the nucleophilic addition of 7 orders of magnitudes implying a ~10 5 rate enhancement. Conversely, the longer the chain, the smaller is the electric field needed to catalyze the reaction. The transition state locations of the various reactions were determined using the slopes of the E a versus E 0 plots as well as the Marcus α values. It turns out the efficiency of electric field catalysis is a function of the transition state location. The latter is the transition state (more endothermic reaction) and the more efficient is the electric field catalysis. Copyright © 2014 John Wiley & Sons, Ltd. The energetics of nucleophilic addition and protonation of polyenes under an electric field was computationally determined. Extrapolating the data for 2.5âMV/cm to 10ânm chain length gave a ~10 5 rate enhancement. It turns out that the efficiency of electric field catalysis is a function of the transition state location. The latter the transition state (more endothermic reaction), the more efficient is the electric field catalysis.

Description: A theoretical study on the nature of hydrogen bond for formamide and its heavy complexes (CYHNH 2 ···XH; Y O, S, Se, Te; X F, HO, NH 2 ) was performed on the basis of density functional theory and the quantum chemistry analysis. Except for the CYHNH 2 ···NH 3 complexes, the substitution of O atom at formamide with less electronegative atoms (S, Se, and Te) is found to weaken the hydrogen bond (H-bond). This substitution results in cyclic structure of hydrated and ammoniated formamide complexes by the formation of bifunctional H-bonds (Y···H 4 X; X···H 3 C). Natural bond orbital analysis indicates that the H-bond is weakened because of less charge transfer from a lone pair orbital of H-bond acceptor to antibonding orbital of H-bond donor. The quantum theory of atoms in molecules analysis reveals that the acyclic structure with single H-bond stabilizes the complexes more than the cyclic structure formed by bifunctional H-bonds. Natural energy decomposition analysis (NEDA) and block-localized wavefunction energy decomposition (BLW-ED) analyses show that the H-bond stabilization energies of NEDA and BLW-ED have good correlation with the dissociation energy of formamide complexes and charge transfer from donor to acceptor atom play an important role in H-bonding. We have also studied the low-lying electronic excited states (T 1 , T 2 , and S 1 ) for CYHNH 2 ···H 2 O complexes to explore the nature of H-bond on the basis of electronegativity and found that NEDA also establishes a good correlation with relative electronic energy (with respect to their ground state) and H-bond strength at their excited states. Copyright © 2014 John Wiley & Sons, Ltd. Hydrogen-bond (H-bond) natures are different in different formamide complexes. They play their role as proton acceptor only in forming H-bond with Lewis acid like HF and preferably form acyclic structure with almost linear alignment. In formamide-H 2 O and formamide-NH 3 complexes, they have a dual role as both H-bond acceptor and H-bond donor and form the cyclic structure. Natural energy decomposition analysis can efficiently evaluate the H-bond strength in formamide complexes at their ground state and their low-lying excited states.

Description: A series of m âterphenylâsubstituted silanes was prepared and studied with regard to the steric and electronic interactions between the silyl core and the terphenyl shroud. Only weak conformational preferences were observed for the core, but the Ïâbasicity of the lateral rings led to distinct nuclear magnetic resonance shifts, and o âfluorine atoms led to throughâspace coupling effects. Copyright © 2014 John Wiley & Sons, Ltd. The steric and electronic interactions between the silyl core and the terphenyl shroud of a series of m âterphenylâsubstituted silanes were investigated by Xâray crystallography, nuclear magnetic resonance spectroscopy, and computation.

Description: The time-dependent density functional theory method was performed to investigate the excited-state hydrogen-bonding dynamics of N-(2-hydroxyethyl)-1,8-naphthalimide (2a) and N-(3-hydroxyethyl)-1,8-naphthalimide (3a) in methanol (meoh) solution. The ground and excited-state geometry optimizations, electronic excitation energies, and corresponding oscillation strengths of the low-lying electronically excited states for the complexes 2a + 2meoh and 3a + 2meoh as well as their monomers 2a and 3a were calculated by density functional theory and time-dependent density functional theory methods, respectively. We demonstrated that the three intermolecular hydrogen bonds of 2a + 2meoh and 3a + 2meoh are strengthened after excitation to the S 1 state, and thus induce electronic spectral redshift. Moreover, the electronic excitation energies of the hydrogen-bonded complexes in S 1 state are correspondingly decreased compared with those of their corresponding monomer 2a and 3a. In addition, the intramolecular charge transfer of the S 1 state for complexes 2a + 2meoh and 3a + 2meoh were theoretically investigated by analysis of molecular orbital. Copyright © 2014 John Wiley & Sons, Ltd. Highlights are as follows: (i) the intramolecular hydrogen bonds within the monomers are broken, and three intermolecular hydrogen bonds are formed in methanol solution; (ii) the intermolecular hydrogen bonds are strengthened upon photoexcitation; and (iii) intramolecular change transfer features are studied.

Description: Cage-cluster complementarity is of crucial importance in determining the sizes and structures, as well as the properties of endohedral fullerenes. The encapsulated atoms or clusters, which are typically in a positively charged state, are irreversibly, mechanically, and electrostatically trapped inside the typically negatively charged cages. These rather exotic compounds exhibit exquisitely complementary properties between their components. Here, we present a short overview to show that size and shape are crucial in determining the specific structures that are formed, and the presence of electrostatic interactions result in structural motifs that are never observed for pristine fullerene cages. Copyright © 2014 John Wiley & Sons, Ltd. Cage-cluster complementarity is of crucial importance in determining the sizes and structures, as well as the properties of endohedral fullerenes. The encapsulated atoms or clusters, which are typically in a positively-charged state, are irreversibly, mechanically, and electrostatically trapped inside the typically negatively-charged cages. Here, we present a short overview to show that the size and shape are crucial in determining the specific structures that are formed and the presence of electrostatic interactions result in structural motifs that are never observed for pristine fullerene cages.

Description: In this work, the corrected total electron density based on ellipticity (ε) at C–C bond critical points in a given ring and bond length alternations was introduced to estimate π-electron density distributions in the ring. Then, to evaluate aromaticity of rings with any number of members, the was normalized relative to a system assumed as a full aromatic, which is named as the corrected total electron density (CTED) aromaticity index. For a wide range of aromatic, nonaromatic and antiaromatic compounds, we have compared CTED index with the other commonly used aromatic indices, such as HOMA, PDI, FLU, NICS and recently introduced EL. CTED index was seen to be in agreement with the defined indices, and with general expectations. Hence, as similar to the other indices except from PDI, we have proposed that CTED index could be applied to study the aromaticity of rings without any restriction in the number of members of rings and used to analyze both the local and global aromatic character of rings as a new aromaticity index. Copyright © 2014 John Wiley & Sons, Ltd. A new aromaticity index based on electron density at bond critical points was introduced. The validity of this index was checked for a series of rings in monocyclic and polycyclic structures.

Description: The gas-phase acidity (GA) of a series of 1,1-bis(trifluoromethanesulfonyl)propane derivatives, Tf 2 CHCH 2 CH(R 1 )R 2 , and Tf 2 CHCH 2 Ar (Ar =  phenol derivatives ) was determined by measuring proton-transfer equilibria using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer and by computing the free energy of the deprotonated carbanions and the corresponding neutrals. The effects of R 1 and R 2 or Ar groups on the acidity were examined. In Tf 2 CHCH 2 CH(R 1 )R 2 , the GA values calculated using the conformers of neutral molecules that are free from the intramolecular hydrogen-bonding interaction between the acidic hydrogen atom of the Tf 2 C H moiety and R 1 or R 2 group and between the hydrogen atom of the C H R 1 R 2 moiety and the SO 2 CF 3 group were correlated in terms of an equation, GA = −17.0Σσ I  + 3.4Σσ α  + 299.5. On the basis of this correlation, it was elucidated that the intramolecular hydrogen bonding or dipole–dipole interaction in the neutral molecule weakens significantly the acidity. In Tf 2 CHCH 2 Ar ( and ), the GA was strengthened by the strong hydrogen-bonding interaction between the phenolic hydrogen in the aromatic moiety and the SO 2 CF 3 group in the conjugate anion compared with that in the neutral molecule. Copyright © 2014 John Wiley & Sons, Ltd. The gas-phase acidity of 1,1-bis(trifluoromethanesulfonyl)propanes, Tf 2 CHCH 2 CH(R 1 )R 2 , and Tf 2 CHCH 2 Ar (Ar = phenol derivatives) was determined experimentally and theoretically. The structural effects on the acidity were elucidated.

Description: The bioreduction of N -oxide compounds is the basis for the mode of action of a number of biologically active molecules. These compounds are thought to act by forming a reactive oxygen species through an intracellular reduction and subsequent redox cycling process within the organism. With these results in mind, the preliminary investigation into the electrochemical reduction of the benzisoxazole 2-oxide ring system was undertaken, with the thought that this class of compounds would reduce in a similar fashion to other N -oxide heterocycles. The electrochemical reduction of 3-phenyl-1,2-benzisoxazole 2-oxide on boron-doped diamond was studied using cyclic and square wave voltammetry as well as controlled potential electrolysis and HPLC for qualitative identification of the reaction products. It was found that the reduction proceeded with an initial quasi-reversible one-electron reduction followed by the very fast cleavage of either the endocyclic or exocyclic N–O bond. Subsequent electron transfer and protonation resulted in an overall two-electron reduction and formation of the 2-hydroxyaryl oxime and benzisoxazole. These results are analogous to those observed in the electrochemical reduction of other heterocyclic N -oxides albeit the reduction of the benzisoxazole N -oxides takes place at a more negative potential. However, these encouraging results warrant further investigation into the reduction potential of substituted benzisoxazole N -oxides as well as to elucidate and characterize the nature of the intermediate species involved. Copyright © 2014 John Wiley & Sons, Ltd. The electrochemical reduction of 3-phenyl-1,2-benzisoxazole 2-oxide on boron-doped diamond was investigated by cyclic and square wave voltammetry as well as controlled potential electrolysis. It was found that the reduction proceeded with an initial quasi-reversible one-electron reduction followed by the very fast cleavage of either the endocyclic or exocyclic N–O bond. Subsequent electron transfer and protonation resulted in an overall two-electron reduction and formation of the 2-hydroxyaryl oxime and benzisoxazole.

Description: Density functional theory calculations were performed for the methanolysis reactions of a set of aryloxy and alkoxy acetates ( ) promoted by methoxide and a 1,5,9-triazacyclododecane-complexed Zn (II) -methoxide [2(OCH 3 )] + in order to give free energies and structural data for the various intermediates and transition states along the reaction pathway. The methoxide-promoted reactions experience a transition of pathways from enforced-concerted addition of CH 3 O − to the C = O unit for substrates having a good aryloxy leaving groups (LGs) with strong electron withdrawers ( ) to a two step process with rate-limiting CH 3 O - attack on aryloxy acetates having higher (the pK a of the parent phenol of the LG in methanol) values. Only in the case of the substrates 1i-m having alkoxy LGs is there an observed change in rate-limiting step that occurs at the quasi-symmetrical point where the . The methanolysis process for the 2,4-dinitrophenoxy substrate ( ) promoted by [2(OCH 3 )] + involves transient binding of the substrate to the metal complex followed by a rate-limiting, enforced-concerted attack of Zn (II) -coordinated – OCH 3 , with fast breakdown of an addition intermediate that does not have a significant lifetime. For substrates 1b,c having slightly less electron withdrawing substituents, the reaction has two steps with rate-limiting attack and an unassisted LG departure. As the increases, the reaction still has two steps with rate-limiting attack, but departure of the LG is now assisted by its coordination to the metal ion. For alkoxy containing substrates, a change in rate-limiting step occurs centered at methoxy acetate, , (when ) for which the second step of metal ion assisted departure of methoxide becomes partially rate-limiting. The Brønsted plots computed for the methoxide-promoted and [2(OCH 3 )] + -promoted methanolyses are compared with the previously determined experimental data and are analyzed as arising not from a common line attributable to all substrates but rather in terms of separate, but intersecting, plots for aryl- and alkyl acetates. Copyright © 2014 John Wiley & Sons, Ltd. Density functional theory computations reveal that a downward break in the Brønsted plot for methanolysis of esters promoted by a Zn-methoxide complex stems from inclusion of esters having both aryloxy leaving groups (LGs) and alkoxy LGs in the same relationship. The plot for aryl esters is shallow showing little sensitivity to the nature of the LG because of a cancellation of effects in the initial complex: substrate binding and those in the subsequent rate-limiting kinetic step. The plot for cleavage of alkoxy-containing esters is steeper and breaks at the quasi-symmetrical point of s s pK a HOLG =18.13.

Description: Stationary point structures (or stable structures) and the electronic states of polycyclic conjugated hydrocarbons are estimated by an extended combination method between two Kekulé structures (ECMK). The estimation by the ECMK required two postulation conditions. (i) Stationary point structures can be represented with one Kekulé structure or the combination of two Kekulé structures. (ii) Structures including element Kekulé structures of the structures with lower energy are not candidates for structures with higher energy. The structures and electronic states of 13 compounds composed of six-cyclic and four-cyclic rings were estimated by the ECMK, and corresponded to their geometries and the local aromaticity obtained by complete active space self-consistent field molecular orbital and B3LYP methods. Copyright © 2014 John Wiley & Sons, Ltd. Stationary point structures (or stable structures) and the electronic states of polycyclic conjugated hydrocarbons are estimated by an extended combination method between two Kekulé structures (ECMK). The estimation by the ECMK required two postulation conditions. (i) Stationary point structures can be represented with one Kekulé structure or the combination of two Kekulé structures. (ii) Structures including element Kekulé structures of the structures with lower energy are not candidates for structures with higher energy. The structures and electronic states of 13 compounds composed of six-cyclic and four-cyclic rings were estimated by the ECMK, and corresponded to their geometries and the local aromaticity obtained by complete active space self-consistent field molecular orbital and B3LYP methods.

Description: Three derivatives of alkyl anthracene covalently bonded to aza-18-crown-6 at the nitrogen position, anthracene(CH 2 ) n , ( n  = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6-31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza-18-crown-6 ( ) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time-dependent density functional theory with the basis set 6-31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza-crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza-crown ether-based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza-crown ether part of indicate that the presence of the alkali metal cations Li + , Na + and K + play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd. Three derivatives of alkyl anthracene covalently bonded to aza-18-crown-6 at the nitrogen position, anthracene(CH 2 ) n , which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6-31+G(d,p) level.

Description: No abstract is available for this article.

Description: Computations for anion, dianions, and trianions of benzene are carried out to study the role of electron correlation in the polydeprotonation of benzene leading to benzene trianions both in the singlet and triplet states. The computations, while assessing the use of polarization and diffuse functions, are performed with Møller–Plesset second-order (MP2) perturbation theory and coupled-cluster theory up to the level of CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p), and with density functional theory (DFT) employing a hybrid, B3LYP, and a meta-hybrid, M05-2X, exchange-correlation functionals with Gaussian basis set 6-311++G(d,p) and correlation consistent basis set aug-cc-pVDZ. The deprotonation energies, including zero-point energy correction, of benzene anion and dianions are found to be highly sensitive to the quantum mechanical method and the basis set used. The formation of dianions and trianions, where the anionic centers lie adjacent to each other, is observed with unusual behavior in the deprotonation energy and the geometrical parameters obtained from the different level of the theories. The two exchange-correlation functionals compared show contrasting and unusual results for the trianionic species particularly for the triplet states, even if the diffuse functions are included in the basis set. Besides this, the ortho-dianion and 1,3,5-trianion are predicted to be ground-state triplet at CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) and DFT/M05-2X/6-311++G(d,p) levels, whereas DFT/B3LYP/6-311++G(d,p) predicts meta-dianion and 1,2,3-trianion to be ground-state triplet where all the anionic centers lie adjacent to each other. Copyright © 2014 John Wiley & Sons, Ltd. The presence of complicated inter-electronic interactions in polyanions of aromatic origin makes these systems highly challenging for the exchange-correlation functionals being developed in the density functional theory. In this study exploring polydeprotonation in benzene, contrasting and interesting trends in the deprotonation energies and geometries of singlet and triplet dianions and trianions of benzene are observed while comparing a hybrid and a meta-hybrid exchange-correlation functional.

Description: The reaction of Fenitrothion with O and N nucleophiles (H 2 O 2 , NH 2 OH, n -butylamine and piperidine) was studied at 25 °C in water containing 2% 1,4-dioxane in the presence of native cyclodextrins (α-, β-, and γ-CD). For all the nucleophiles, the presence of CD produces reaction inhibition with saturation kinetics. The greatest effect in all cases is observed with β-CD, and the greatest inhibition was observed for the reaction of Fenitrothion with H 2 O 2 (81%), which is the most efficient nucleophile in promoting Fenitrothion degradation in homogeneous media. In the absence of CD, competition between the S N 2(P) and the S N 2(C) pathways was observed with piperidine as was reported before for the reaction with NH 2 OH and n -butylamine. The presence of β-CD does not modify product distribution in the case of the reaction with NH 2 OH and n -butylamine, whereas there is an increase in S N 2(C) pathway when the nucleophile is piperidine. Copyright © 2014 John Wiley & Sons, Ltd. The presence of β-CD inhibits the reaction of Fenitrothion with O and N nucleophiles. With N nucleophiles, competition between S N 2(P) and S N 2(C) pathways is observed. The effect of β-CD on product distribution depends on the nucleophile.

Description: The structure and dynamics of five-coordinate iridacyclopentadiene–chlorido and –hydrido complexes of the form [(PH 3 ) 2 Ir(CY = CYCY′ = CY′)X] (X = Cl or H and Y = F and/or H) are investigated by M06-2X/Def2-TZVPP density functional theory computation. For the symmetrically substituted ring systems (Y = Y′ = H and Y = Y′ = F) the minimum energy chlorido structures are Y-shaped trigonal bipyramids; whereas the hydrido complexes favor a T-structure. Both the symmetrically and unsymmetrically (Y = H, Y′ = F) substituted hydrido complexes exhibit double well potentials for the hydrido ligand wag motion within the metallacycle ring plane, the depths of the well depending on the degree of steric, and electronic interactions within the particular constitutional isomer. Copyright © 2014 John Wiley & Sons, Ltd. M06-2X/Def2-TZVPP computation reveals that iridacyclopentadiene complexes of the form [(PH 3 ) 2 Ir(CH = CHCF = CF)H] exhibit double well potentials for the hydrido ligand wag motion within the metallacycle ring plane, the depths of the well depending on the degree of steric, and electronic interactions within the particular constitutional isomer.

Description: Graphene oxide (GrO) prepared by the Hummers method was separated into three different fractions (GrO 5000 , GrO 2000 , and GrO res ) on the basis of their dispersion stability in the water. Infrared, nuclear magnetic resonance , X-ray photoelectron spectroscopy , and elemental analyses revealed that GrO 5000 possesses a high degree of oxygen functionalities including phenolic, carboxylic, and −OSO 2 H groups, compared with the other fractions. The GrO 5000 was found to be a highly efficient and reusable solid catalyst for the esterification of various carboxylic acids with a variety of alcohols to furnish corresponding esters in high to excellent yields. The catalytic activity of the GrO 5000 was attributed to the ability of highly polar GrO 5000 scaffold to adsorb/attract reactants, where the acid functionalities of GrO 5000 facilitated the esterification process efficiently. The chemical and structural features of GrO 5000 were discussed to understand the improved catalytic activity compared with GrO 2000 and conventional solid acid catalysts. Copyright © 2014 John Wiley & Sons, Ltd. Graphene oxide (GrO) prepared by the Hummers method was fractionally distributed on the basis of their dispersion stability in water, and then, the catalytic activities of GrO fractions were explored for esterification reaction. The presence of acidic functionalities in GrO along with its excellent dispersibility in reaction media was found to afford high catalytic conversion. The chemical and structural features of GrO have been discussed to understand the catalytic activity.

Description: The chlorination reactions of nitrogenous organic compounds (2,2,2-trifluoroethylamine, benzylamine, glycine, and dimethylamine) by tert -butyl hypochlorite ( t BuOCl) were studied at 25 °C, ionic strength 0.5 M and under isolation conditions. The kinetic results obtained in the formation processes of the corresponding N -chloramines in acid medium (pH = 5–7) are summarized in this paper. Kinetic studies showed a first order with respect to t BuOCl concentration. The chlorination reactions involving benzylamine, glycine and dimethylamine were all first order with respect to nitrogenous compound concentration and approximately −1 order with respect to proton concentration. The reaction with 2,2,2-trifluoroethylamine was more complex, and the order of reaction with respect to the amine varied with pH. Copyright © 2014 John Wiley & Sons, Ltd. The kinetic behavior of 2,2,2-trifluoroethylamine, benzylamine, glycine and dimethylamine with tert -butyl hypochlorite was studied. Free-energy relationships were established during the results obtained and others available in the literature for reaction with HOCI, N -chlorosuccinimide and N -chloro- N -methyl-p-toluensulfonamide.

Description: High-spin organic molecules have attracted much attention as spin sources for magnetic materials . In this paper, a novel high-spin organic molecule was designed according to a logical strategy. A 2,2-dimethylcyclopentane-1,3-diyl diradical unit was utilized as a spin source and a spin-bridged fragment. In addition, nitroxides were introduced as spin sources. Quintet electron-spin resonance (ESR) signals, which were attributed to the 1,3-di(3′-nitoroxyphenyl)-2,2-dimethylcyclopentane-1,3-diyl tetraradical ( ), were observed in a 2-methyltetrahydrofuran glassy matrix at 80 K after the photodenitrogenation of a newly synthesized azoalkanes . A simulation of the signal provided the zero-field splitting parameters D (| D |/hc = 0.0127 cm −1) and E (| E |/hc = 0.0014 cm −1 ) for the quintet state of the tetraradical . The parameter D of the quintet state of was found similar to those of the previously reported quintet spin states of tetraradical with two cyclobutane-1,3-diyl units (0.0190 cm −1 ) and with two 2,2-dimethylcyclopentane-1,3-diyl diradicals (0.0116 cm −1 ). Copyright © 2014 John Wiley & Sons, Ltd. Quintet electron-spin resonance signals, which were attributed to the 1,3-di(3′-nitoroxyphenyl)-2,2-dimethylcyclopentane-1,3-diyl tetraradical, were observed in a 2-methyltetrahydrofuran glassy matrix at 80 K after the photodenitrogenation of a newly synthesized azoalkane. A simulation of these signals provided the zerofield splitting parameters D (| D |/hc = 0.0127 cm −1 ) and E (| E |/hc = 0.0014 cm −1 ) for the tetraradical.

Description: No abstract is available for this article.

Description: The photochemistry of diphenylcarbene , matrix-isolated in argon at 3–5 K was investigated by UV–Vis, IR, and EPR spectroscopy. Although carbene proved to be stable toward broadband UV irradiation, it slowly rearranges to 1-phenyl-1,2,4,6-cycloheptatetraene during irradiation with the intense light of a 445-nm diode laser. Other intermediates were not observed. Allene is the key intermediate that was missing in the proposed mechanism of the rearrangement of to fluorene . Copyright © 2014 John Wiley & Sons, Ltd. Matrix-isolated diphenylcarbene ( 5 ) is stable towards broadband UV irradiation, in contrast to the highly photolabile phenylcarbene, which readily rearranges to cycloheptatetraene. The corresponding 1-phenyl-1,2,4,6-cycloheptatetraene ( 8 ), which is a key intermediate in the rearrangement of carbene 5 to fluorene 7 , could now be generated in an argon matrix by irradiation of carbene 5 with the intense 445-nm light of a diode laser.

Description: We have isolated two isomeric solids and of N , N ′-bis(3,5-dichlorosalicylidene)-2,2′-ethylenedianiline and characterized by IR, UV/Vis, X-ray powder diffraction , thermogravimetric analysis/differential thermal analysis, and X-ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid ( ) shows endo conformation while yellow solid ( ) exhibits exo form depending on packing modes. UV/Vis spectra of and appear very similar patterns in the solid state; however, the bands of are slightly red-shifted compared with those of . displays a strong fluorescent emission band at ~582 nm while shows an intense fluorescent signal at ~563 nm. The charge density populations of and have been studied by computational simulations using density functional theory at pbe1pbe/6-311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of and confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO-LUMO in is smaller slightly than that of about 0.05 eV (~17 nm). Copyright © 2014 John Wiley & Sons, Ltd. The endo ( 1 ) and exo ( 2 ) conformational isomers of N,N ′ bis(3,5-dichlorosalicylidene)-2,2′-ethylenedianiline were isolated in ethanol and characterized. Both compounds display different colors and luminescence behaviors. The difference of λ max values of 1 and 2 in photoluminescence is in good agreement to the difference of highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps of 1 and 2 .

Description: A large body of data exists about the interaction between curved π systems and C 60 or C 70 . However, little is known about the interaction with fullerenes smaller than C 60 or larger than C 70 . To fill that gap, we studied, by means of density functional theory (M06-2X), the interaction between corannulene, pentaindenocorannulene, C 60 H 28 buckycatcher and the following fullerenes: C 44 , C 50 , C 80 , C 90 , C 100 , C 180 and C 240 . For fullerenes smaller than C 60 , their high reactivity facilitated the covalent addition to the hosts assayed. Yet, the reaction energies determined for the covalent addition were comparable to those calculated for the formation of supramolecular complexes. Thus, the receptor may host a fullerene and at least have another one attached. As expected, for fullerenes larger than C 70 , supramolecular complexes were preferred over covalent assemblies. The binding energies with bowls increased with the size of the fullerenes in a non-monotonic fashion since they depended on the shape of the fullerene. Indeed, for one C 80 isomer, it is possible to find a region which forms a complex with corannulene that is stronger than C 60 @corannulene, while another region exists whose interaction with corannulene is weaker. As the size of the fullerene becomes larger, ball–socket interactions are weakened, and CH–π interactions become important, accounting for the large interaction determined for corannulene and graphene. Finally, for the buckycatcher, the maximum encapsulation energy among the fullerenes assayed was displayed by C 90 . The fullerenes C 80 , C 90 and C 100 formed complexes with the buckycatcher which are stronger than in C 60 @buckycatcher. Copyright © 2014 John Wiley & Sons, Ltd. The strength of the stacking interaction between well-curved pi systems and fullerenes larger than C 70 depends on the shapes of the fullerene and the host. For C 80 , a region can bind to corannulene more strongly than C 60 , but a different region can do so more weakly. C 90 displayed the best fit with the famous C 60 H 28 buckycatcher.

Description: Electron and hydrogen transfers are basic steps in many chemical reactions. Photochemical or electronic excitation significantly influences the reactivity of chemical compounds and thus also these transfer processes. Furthermore, the formation of typical intermediates has a decisive impact on the outcome of the transformations. Based on these properties of photochemical processes, efficient homogeneous and heterogeneous photocatalytic transformations for application to organic synthesis have been developed. Efficient reactions without any chemical activation but induced by photochemical electron transfer can also be carried out. The photon acts as a traceless reagent. In the context of photochemical hydrogen transfer, two processes are frequently encountered. The two particles the electron and the proton are transferred either simultaneously or in two steps. In the latter case, the electron is transferred first and the proton follows. Both processes are applied to organic synthesis. Copyright © 2014 John Wiley & Sons, Ltd. Photochemically induced proton and electron transfers play an important role in many organic photochemical reactions. The way in which they are transferred has a significant influence on the outcome of these reactions. In this context, photochemical-induced hydrogen transfer is described as a sequence of transfers of both particles.

Description: Photolabile protecting groups have been extensively studied and applied for protection of small biological molecules, which make it convenient to detect the biological processes of the caged compounds. In this study, a series of 8-nitroquinoline-based photolabile caging groups for carboxylic acid were synthesized with improved photolysis efficiency. Among them, 6-bromo-8-nitro-1, 2-dihydroquinolinyl chromophore was proven the best derivative on account of its longest absorption wavelength (345 nm), highest caging ability, and quantum yield ( Φ  = 0.003). Moreover, density functional theory calculations were performed in order to study the photolysis mechanisms. Theoretical calculations revealed that the reaction was kinetically inert under general mild condition with the high barrier height of 34.3 kcal/mol at carbonyl migration step, while under the photolysis condition, because of the large energy gap (64.5 kcal/mol) between S 0 and S 1 states, the reaction should be accessible in the triplet ground state ( T 1 ) through successive excitation of S 0     S 1 states, subsequent intersystem crossing of S 1     T 1 states, and finally returned to the stable  S 0 state for product via potential energy surface crossing between T 1 and S 0 states. Copyright © 2014 John Wiley & Sons, Ltd. Theoretical calculations support a mechanistic pathway involving the micro-processes of excitation of S 0     S 1 states, intersystem crossing between S 1 and T 1 states, reacting on the surface of T 1 state, and finally, return to the S 0 state through potential energy surface.

Description: The objective of this work is to provide an in-depth interpretation of the electronic structures and optical properties of diindolocarbazole isomers. A systematic study of these different structures caused by the linkage pattern was performed via theoretical calculations. The optimized geometries, electronic properties, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, and absorption and emission spectra of these isomers have been calculated and analyzed. Based on the detailed comparisons, the diindolocarbazoles act as candidates of different functional materials for optoelectronic application was predicted and the theoretical reference for the synthesis efforts and experimental investigation was provided. Copyright © 2014 John Wiley & Sons, Ltd. A systematic study of the electronic structures and optical properties of diindolocarbazole isomers was performed via quantum chemistry calculations. The optimized geometries, electronic properties, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, and absorption and emission spectra of these isomers have been calculated and analyzed. On the basis of the detailed comparisons, the diindolocarbazoles act as candidates of different functional materials for optoelectronic application was predicted, and the theoretical reference for the synthesis efforts and experimental investigation was provided.

Description: We carried out molecular dynamics (MD) simulations with the AMBER force field for four pairs of spherical dimers of different size (neopentane, bicyclooctane, adamantane, and fullerene-C 60 ) using the TIP3P model of water as solvent. For comparison, we performed MD simulations for a linear molecule of n-pentane at the same conditions. To assess the entropy contribution to the Gibbs free energy, MD simulations were run at three different temperatures of 273 K, 323 K, and 348 K, respectively, using umbrella-sampling/the WHAM method. The stability of dimers is described by a potential of mean force (PMF). The shape of PMF curves for hydrophobic interactions is characteristic, and entails a contact minimum, a solvent-separated minimum, and a desolvation maximum. The depth and position of the contact minimum for each pair change with the size of the nonpolar particle, and are consequently shifted to a larger distance for larger molecules. Additionally, the Lennard–Jones contribution to the PMF increases simultaneously with an increase in particle size. For a linear dimer, the contact minimum is shifted to a shorter distance than it is for spherical systems with the same number of carbon atoms. The contact minima on PMF curves increase with temperature, suggesting that the association entropy is positive. Dimensionless PMF curves showed a low dependency (near contact minima regions) on temperature, as the association entropy is low. Copyright © 2014 John Wiley & Sons, Ltd. The behavior of spherical hydrophobic dimer, such as neopentane pair in water, is described by potential of mean force (PMF). The entropic and energetic factors to PMF could explain the nature of the hydrophobic association process.

Description: Absolute rate constants for hydroxyl radical, azide radical, and hydrated electron reactions with a sulfa drug 4,4'-diamino diphenyl sulfone (dapsone) in water have been evaluated using electron pulse radiolysis technique. Absolute rate constants for hydroxyl radical and azide radical were determined as (8.4 ± 0.3) × 10 9 and (5.6 ± 0.5) × 10 9  M −1  s −1 , respectively. The reduction of dapsone with the hydrated electron occurred with rate constant of (9.2 ± 0.1) × 10 9  M −1  s −1 . Hydroxyl radical reactions result in the synchronous formation of adduct as well as anilino radical. The interesting observation is that the yield of the anilino radical increases with increase in pH. Contrary to this, the yield of the adduct decreases with pH. We propose that hydroxyl radical adds predominantly to the aniline. In contrast, the reaction of azide radical with the dapsone suggests that the reaction occurs at the –NH 2 moiety of the aniline ring. The free radical electron transfer from dapsone to parent radical cation of non-polar solvent also results in the formation of anilino radical only suggesting that the radical cation of dapsone has a short lifetime. The reaction of hydrated electrons with the dapsone suggests that the reaction occurs at different reaction site. The experimental results supported by theoretical calculations of this study provide fundamental mechanistic parameters that probably decide the fate of the radical cation of aniline derivatives. Copyright © 2014 John Wiley & Sons, Ltd. Correlations of calculated Gibbs free energy ΔG and reaction enthalpy ΔH of N-centred radical formation through deprotonation for aniline, dapsone, p-amino benzhydrazide, m-amino benzhydrazide, benzidine, o-tolidine, 3,3'-5,5'-tetramethyl benzidine, and N,N'-diphenyl benzidine.

Description: A scheme for the p K a estimation of organic acids in dimethylsulfoxide (DMSO) solution based on quantum chemical calculations is proposed. The procedure of p K a calculation requires several steps. The first is the calculation of the gas phase acidity of the compound. The G3MP2B3, G4MP2 as well as CBS-QB3 composite methods made it possible to estimate values of gas phase acidities of an extensive set of structures with a high confidence level (standard deviations equal to 1.15, 1.13 and 1.29 kcal mol −1 , respectively; the test set included 91 compounds). The second step is the computation of the solvation correction with the integral equation formalism version of polarizable continuum model (IEF-PCM)–B3LYP/6-311+G(d,p) approximation. Within the bounds of our approach, the medium properties were covered only by the PCM model, i.e. the proposed procedure neglects specific interactions between DMSO and the solute. It was determined that the approach to p K a estimation mentioned above is the most balanced in terms of accuracy, resource intensity and computation time cost. In the third step, the error of the p K a calculation was decreased by correlation allowances. Correlation allowances were determined for each acid class (62 С―Н, 55 N―Н, 24 O―Н and 5 S―Н acids) in the range of 50 units in terms of logarithmic scale using the test set including 146 compounds. Seven O―H acids showing the ability to form cyclic dimers were separated into a discrete group. The proposed methodology was applied to the estimation of p K a for trans - and cis -dimethyl-4,5-dihydro-3 H -pyrazol-3,5-dicarboxylates as well as for 5-fluorouracil subject to competitive dissociation, the latter by N1―H or N3―H bonds. Copyright © 2014 John Wiley & Sons, Ltd. The proposed calculation procedure of p K a for the condensed phase (DMSO) is based on the correction of gas phase acidities (G3MP2B3) by the solvate factor estimated in the (IEF-PCM)–B3LYP/6-311+G(d,p) approximation. The test set was divided into five groups. Every group of X-centered acids (X = C, N, O (as well as dimers of O―H acids), S) had individual regression coefficients.

Description: The binding behavior of a cavitand introduced by de Mendoza is explored with new guest species. Dimerization to hydrogen-bonded capsules occurs in the presence of appropriate guests, including alkanes, alkylated arenes, stilbenes, benzanilides, and carbodiimides. Peripheral tetraethylene glycol groups are attached to the cavitand to improve solubility. Encapsulation of hydrophobic compounds can be observed in aqueous media. Copyright © 2014 John Wiley & Sons, Ltd. The behavior of the capsule 1.1 in solvents that compete for hydrogen bonds was examined. Methanol in mesitylene dissolved aggregated capsules and gave discrete encapsulated species as shown by nuclear magnetic resonance spectroscopy. Replacement of the alkyl “feet” with tetraethylene glycols produced more soluble capsules.

Description: The understanding of the electronic effects of the diastereoselective addition of a nucleophile to a polar substituted aldehyde or ketone is not complete, with several theories competing to explain the data. For numerous hydride reductions of 3-X-2-butanones (X = F, Cl, Br), the selectivity for the major syn isomer is significantly and consistently higher for X = Br than for X = F. This result is rationalized as a shift in mechanism from Cornforth (X = F) to Felkin–Anh (X = Br). The experimental data is well modeled by ab initio calculations for the addition to these ketones by BH 3 , but not by other nucleophiles such as LiH or LiAlH 4 . The energetic ordering of the BH 3 transition states largely follows the trends for the ground state ketones. Here, consistent with electrostatic arguments, the anti orientation of the C―X and C O bonds is always lower in energy than the syn arrangement. The gauche conformer is intermediate between these two, becoming gradually lower in energy as X increases in size. The hyperconjugative interaction invoked by the Felkin–Anh model provides only a modest stabilization of the relevant transition states as judged by NBO analysis. Copyright © 2014 John Wiley & Sons, Ltd. Evidence is presented showing that at least two models, Felkin–Anh and Conforth, are needed to explain diastereoselectivity in nucleophilic addition to polar ketones. The hyperconjugative explanation given by Anh is challenged.

Description: Potential carbene precursors have been considered for three tetracyclic benzene isomers: carbene for tetracyclo[3.1.0.0 1,3 .0 3,5 ]hexane, ; carbene for tetracyclo[3.1.0.0 1,4 .0 2,3 ]hexane, , considered by Loschmidt as a structure for benzene; and carbene for Ladenburg's prismane, . The bicyclic (CH) 6 isomer, , avoids intramolecular cycloaddition ; it is converted instead to Dewar benzene, ; the system – is a “foiled” carbene system; finally, we were unable to characterize the putative precursor, , for Loschmidt's hydrocarbon; an attempt to generate it by adding an electron to the corresponding carbene cation, , resulted in conversion to anti -10. The trajectory of this conversion indicates that “ ” lies at or below the inflection point of the trajectory connecting a putative transition state with anti - . The free energies of all six species lie in the range 120–165 kcal/mol, well above any species that may be involved in the topomerization of benzene. Copyright © 2014 John Wiley & Sons, Ltd. The putative carbene precursor (A) for Loschmidt's tetracyclic C6H6 hydrocarbon (B) proved to be elusive. An attempt to generate it by adding an electron to the corresponding carbene cation resulted in conversion to the anti-isomer of the tetracyclic hydrocarbon. The trajectory of this conversion indicates that ”B“ lies at or below the inflection point of the trajectory connecting a putative transition state with the anti-hydrocarbon .

Description: This review outlines fundamental factors responsible for hybridization trends in organic and main group compounds. Hybridization is a classic chemical concept that transcends textbook organic chemistry. Hybridization effects are omnipresent, and their understanding is essential for the unraveling of many structural and reactivity puzzles. Even when they are masked by a stronger effect (e.g., allylic delocalization), they still lurk below the surface. Overriding such effects comes with a penalty, whereas incorporation into reaction design provides an efficient tool for the control of reactivity. Copyright © 2014 John Wiley & Sons, Ltd. This review outlines fundamental factors responsible for hybridization trends in organic and main group compounds. Hybridization effects are omnipresent, and their understanding is essential for the unraveling of many structural and reactivity puzzles. Even when they are masked by a stronger effect, they still lurk below the surface.

Description: The BN-phenanthryne dibenz[c,e][1,2]azaborine (9) was previously inferred as a reactive intermediate in the solution phase thermolysis of 9-azido-9-borafluorene by isolation of its cyclic tetramer. The mechanism of the cyclotetramerization of BN-phenanthryne (9) is investigated using a meta-generalized gradient approximation density functional (TPSS-D3) in conjunction with a polarized split valence basis set and single energy points using a double-hybrid functional (B2PYLP-D3) with a polarized triple-zeta basis set. The most favorable mechanism involves the dimerization of 9 to diazadiboretidine derivative , followed by dimerization of for which two different pathways were identified computationally. The more favorable one involves a B 4 N 4 bicyclo[4.2.0]octa-2,4,7-triene intermediate . An alternative mechanism, slightly higher in energy, proceeds through a B 4 N 4 cube isomer that lies in an unexpectedly deep potential energy minimum. The low barriers of dimerization of make it a short lived reactive intermediate that likely is too reactive to be trapped by the still more reactive cyclic iminoborane 9. Copyright © 2014 John Wiley & Sons, Ltd. The cyclotetramerization of BN-phenanthryne may proceed via a B4N4 cube isomer or through a mechanism involving conventional intermediates.

Description: Laser flash photolysis of cyclopropyl(phenyl)methanone 6 in argon-saturated methanol yields the triplet ketone (T 1K ) of 6 that is formed with a rate constant of ~1.7 × 10 7  s −1 ( λ max  = 360 nm) and has a lifetime of ~1.4 µs. T 1K of 6 decays to form ketyl radical 7 ( λ max ~300 nm), which dimerizes to form photoproducts, pinacol derivatives 8 and 9. In comparison, photolysis of trans -phenyl(2-phenylcyclopropyl)methanone 1 in argon-saturated chloroform-d results in cis -phenyl(2-phenylcyclopropyl)methanone 2 and a smaller amount of 3, presumably through 1,3-biradical 11. Nanosecond laser flash photolysis of 1 does not reveal significant transient absorption, although the T 1K of 1 is detected with phosphorescence at 77 K. Density functional theory calculations were used to elucidate the triplet reactivity of 1, 2 and 6 by comparing the feasibility of H atom abstraction, cyclopropyl cleavage and β-quenching of their triplet ketones. Copyright © 2014 John Wiley & Sons, Ltd. Irradiation of α-cyclopropyl(phenyl)methanone results in H atom abstraction and formation of ketyl radical that was characterized directly with laser flash photolysis. In comparison, photolysis of trans-phenyl(2-penylcyclopropyl)methanone results in cis-trans isomerization that presumably takes place through short lived 1,3-biradical.

Description: The different electronic states of trications and tetracations have been studied for oligomers made of n 3,4-ethylenedioxythiophene units, where n ranges from 2 to 30. Results have been compared with those obtained for neutral, monodications and dications of the same n -oligomers. For the longer oligomer ( n  ≥ 24) trications, the doublet and quartet states are isoenergetic, while the triplet and quintet states are isoenergetic for tetracations of the same length. Analysis of the geometry reveals three separated polarons for the doublet and quartet states of tricationic n -oligomers, even though that of the former state has been attributed to a heavy spin contamination. In contrast, the structure of tetracations shows double bipolaron character for the singlet state and two polaron pairs for both the triplet and quintet states. Analyses of both charge and spin density distributions support the polaronic or bipolaronic behavior predicted by molecular geometry for the different electronic states. Results have been also used to evaluate the ionization potentials and the π-π * lowest transition energy of infinite polymer chains. Copyright © 2014 John Wiley & Sons, Ltd. Geometrical, electronic and energetic properties of n -EDOT trications and tetracations have been evaluated using U-DFT calculations with three different functionals. The doublet and quartet states of n -EDOT +3 show three separated polarons, whereas n -EDOT +4 show double bipolaron for the singlet state and two polaron pairs for both the triplet and quintet states. The doublet and quartet states of n -EDOT +3 are isonergetic, while the triplet and quintet states are isoenergetic for n -EDOT +4 of the same length.

Description: For the past 60 years, the standard model for the interpretation of the mechanism for proton transfer has been based upon transition-state theory, which posits that the transition state is found in the proton transfer coordinate involving the breaking and making of bonds. However, the observed dynamics of proton transfer within the triplet contact radical ion pair, derived from a variety of substituted benzophenones complexed with N , N -dimethylaniline, cannot be accounted for within the standard model for proton transfer. Instead, the kinetic behavior is in accord with nonadiabatic proton transfer theory that has the transition state in the solvent coordinate. Evidence for the importance of the solvent coordinate comes from the existence of an inverted region; as the driving force for reaction increases, the rate of proton transfer decreases. This kinetic behavior is not found in the standard model. The present paper employs density function theory to examine the question as to whether the inverted region can be attributed to the transition state being in the solvent coordinate or whether the inverted region is an artifact produced by changes in the structure of the triplet contact radical ion pair with the placement of substituents upon the p , p ′ positions of benzophenone. It is concluded that the inverted region is not an artifact of substituent effects upon structure. These results support the conclusion that the transition state for proton transfer resides in the solvent coordinate and challenges the validity of the standard model for interpreting the mechanism of proton transfer. Copyright © 2014 John Wiley & Sons, Ltd. The structure and energetics for nonadiabatic proton transfer in the contract radical ion pairs derived from substituted benzophenone/ N , N -dimethylaniline are investigated using density functional theory. The previously observed decrease in rate constant for proton transfer with driving force, the inverted region, is found not to be an artifact of substituents perturbing the structure of the reacting species. Rather, the inverted region arises from the transition state for proton transfer being in the solvent coordinate and not in the proton transfer coordinate as usually assumed.

Description: Herein, we describe diverse reactivity of (anthracen-9-yl)methanamines with a few electron-deficient acetylenes. Depending on the solvent and concentration, (anthracen-9-yl)methanamines reacted with acetylenes through one electron transfer, two electron transfer, or Diels–Alder pathways; and under certain conditions, we observed multiple reaction pathways. We have proposed plausible mechanisms to account for various reactions observed by us. Copyright © 2014 John Wiley & Sons, Ltd. Effects of reagent concentration and nature of solvent on the reactions between anthracenemethanamines and electron-deficient acetylenes are described. Competition between single electron transfer, Michael-type addition, and cycloaddition pathways is observed in these reactions.

Description: The intramolecular С=O Si coordination in H-complexes of (acetoxymethyl)trifluorosilane and (benzoyloxymethyl)trifluorosilane with proton donors HCl, PhOH, MeOH, and CHCl 3 was investigated by density functional theory and second-order Møller-Plesset perturbation theory (MP2) methods. Interrelation and mutual influence of the intramolecular coordination bond С=O Si and intermolecular hydrogen bonds C=O···H and Si–F···H in H-complexes was established using the AIM and NBO analyses. The С=O Si coordination is weakened by the C=O···H hydrogen bonding but enhanced by the Si–F ax ···H hydrogen bonding. The structure of H-complexes of (acetoxymethyl)trifluorosilane with proton donors in solution was determined by comparing the ν(C=O) and ν(Si–F) frequencies calculated using the conductor-like polarizable continuum model and their experimental Fourier transform infrared values. Copyright © 2014 John Wiley & Sons, Ltd. The intramolecular O Si coordination in the molecules of (acetoxymethyl)trifluorosilane and (benzoyloxymehyl)trifluorosilane and formation of their complexes with H-donors was investigated by the methods of quantum chemistry and FTIR spectroscopy. The interplay between the intramolecular O Si coordination bond and the intermolecular O···H and F···H h-bonds was analyzed. The structure of H-complexes of (acetoxymethyl)trifluorosilane with H-donors in solution was determined by comparing the experimental FTIR frequencies with those calculated using C-PCM model.

Description: A stable Lewis base-free gallole bearing a bulky Mes* group (=2,4,6-( t -Bu) 3 C 6 H 2 ) was synthesized by the treatment of Mes*GaCl 2 with a 3,6-dilithio-3,5-octadiene derivative. Reduction of the gallole with lithium metal afforded the corresponding gallole dianion species as a lithium salt. Structures of the gallole and the lithium salt of the gallole dianion have been elucidated by using X-ray crystallographic analysis, NMR spectroscopies, and density functional theory calculations. Copyright © 2014 John Wiley & Sons, Ltd. A stable Lewis base-free gallole was synthesized. Reduction of a stable gallole with lithium metal afforded the corresponding gallole dianion as the lithium salt, indicating the electron acceptability of the gallole. Structure of the lithium salt of the gallole dianion has been investigated.

Description: The phenyl acetylene and benzyl azide cycloaddition reaction in water in the presence of β-cyclodextrin (β-CD) as a phase transfer catalyst (PTC) can get a better yield in a shorter time. The interaction between β-CD and phenyl acetylene or benzyl azide plays an important role in this reaction. This paper studies the complexes of β-CD with phenyl acetylene and benzyl azide using density functional theory (DFT) method. In order to find out the orientations of guests in the cavity of β-CD, binding energy and deformation energy are investigated, and the calculated results are confirmed by 1 H nuclear magnetic resonance ( 1 HNMR). The data from single point energy indicate that the inclusion complexes can improve the solubilities of phenyl acetylene and benzyl azide in water. The 13 C and 15 N spectra show that the most obvious variation concentrates on C 6 and C 8 of phenyl acetylene and N 15 of benzyl azide in complexes. Mulliken charge and frontier orbital are employed for revealing the charge distribution. The effect of β-CD is discussed in terms of the calculated parameters. Copyright © 2014 John Wiley & Sons, Ltd. The interaction between β-CD and phenyl acetylene or benzyl azide plays an important role in cycloaddition reaction. This paper studies the complexes of β-CD with phenyl acetylene and benzyl azide using density functional theory (DFT) method. The effects of β-CD in CuAAC reaction are discussed in terms of the calculated parameters.

Description: New allene compounds, and , bearing 1,8-dichloroacridene moieties were synthesized, and the oxidation of and was performed to generate thermally stable triplet carbenes. Since the oxidation resulted in the formation of decomposition products, the photolysis of brominated allene compound was performed. UV–vis measurement at low temperatures indicated the generation of intermediates with decreasing starting material , although the efficiency of photolysis was quite low. ESR and electron spin transient nutation (ESTN) spectra suggested that the multiplicity of intermediates is triplet, probably the target triplet carbene is generated. In terms of | D | values of the intermediates, ESR showed that unpaired electrons are more effectively delocalized in by the introduction of nitrogen atoms in the skeleton (biradical character in Scheme 1). The observed triplet species was not stable enough to isolate. Copyright © 2014 John Wiley & Sons, Ltd. Photolysis of a brominated allene compound resulted in the generation of an intermediate, in which unpaired electrons are suggested to be effectively delocalized (biradical form).

Description: Computational studies are reported for reactions of 4-substituted-1-chloro-2,6-dinitrobenzenes 1 , 6-substituted-1-chloro-2,4-dinitrobenzenes 2 and some of the corresponding 1-phenoxy derivatives 3 and 4 with aniline in the gas phase. The effects of substituent groups in the calculated energy values for reactants 1–4 , transition states structures, intermediates and products formed in the reactions between the compounds and anilines have been compared. Calculated bonds length and angles from optimized structures of the reactants were comparable with values reported for some of compounds 1–4 obtained by X-ray crystal structures analysis. Generally, the decomposition of the Meisenheimer intermediate to the products requires more energy compared with the reactants except for when R = H. The order of stabilization of the intermediate was found to reflect the relative order of activation by substituents in the substrates. The 4-substituted-1-chloro-2,6-dinitrobenzenes 1 and the phenoxy derivatives 3 were found to be more stable than their corresponding 6-substituted analogues. This is an indication that the rate of nucleophilic attack at 1-position will increase with increasing ring activation but may be reduced by steric repulsion at the reaction centre that increases in the order Cl 〈 OPh. However, the steric hindrance to the steps involved in nucleophilic substitution by aniline is significantly increased when the substrates contain two ortho-substituents. In most cases, the rate determining step is the decomposition of the σ-adduct intermediate except with 1-chloro-2,6-dinitrobenzenes 1 and 6-substituted-1-chloro-2,4-dinitrobenzenes 2 , either because of reduction in ring activation or the presence of bulky ortho-substituents in the chloro compounds 1 and 2 . Copyright © 2014 John Wiley & Sons, Ltd. Computational studies are reported for reactions of 4-substituted-1-chloro-2,6-dinitrobenzenes 1, 6-substituted-1-chloro-2,4-dinitrobenzenes 2 and some of the corresponding 1-phenoxy derivatives 3 and 4 with aniline in the gas phase. The effects of substituent groups in the calculated energy values for reactants 1–4, transition states structures, intermediates and products formed in the reactions between the compounds and anilines have been compared. Calculated bonds length and angles from optimized structures of the reactants were comparable with values reported for some of compounds 1–4 obtained by X-ray crystal structures analysis.

Description: Descriptors of the heteroatom incorporation effect in the ring-junction position, sEDA(III) and pEDA(III), are introduced for the first time. They express the change in the σ and π valence electron population produced by the heteroatom. The sEDA(III) descriptor is a good measure of electronegativity of ring-junction incorporants. Unexpectedly, the pEDA(III) descriptor does not correlate with π-electron characteristics because the ‘aromatic’ bond pattern in the considered fused ring systems depends on the incorporants' change within the group or period of the periodic system. We found that the HOMA aromaticity index of conjugated paths is useful to trace π-electron flows in heteroatom-incorporated polycyclic (aromatic) systems. Copyright © 2014 John Wiley & Sons, Ltd. Descriptors of the heteroatom incorporation effect in the ring-junction position, sEDA(III) and pEDA(III), are introduced. They express change in the σ and π valence electron population produced by the heteroatom.

Description: Six dyes with N , N -dimethylaminophenyl and 4-nitrophenyl or 2,4-dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges (C C, C N, and N N) connecting the electron-donor and the electron-acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The solvatochromic band observed in each spectrum for the dyes is due to a π ➔ π* transition, of an intramolecular charge transfer nature, which occurs from the electron-donor N , N -dimethylaminophenyl group to the electron-acceptor group in the molecules, which is reinforced by the structures of the compounds optimized by applying density functional theory, which exhibit high planarity. The reverse solvatochromism was explained considering two resonance structures. The benzenoid form is better stabilized in less polar solvents and characterizes the region displaying positive solvatochromism, while the dipolar form is better stabilized in more polar solvents, in the region of negative solvatochromism. The Catalán multiparametric approach was used to study the contribution of solvent acidity, basicity, dipolarity, and polarizability to the solvatochromism exhibited by the compounds. These compounds are good candidates for the investigation of the polarizability and, to a lesser extent, the dipolarity of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding. Copyright © 2014 John Wiley & Sons, Ltd. Six dyes with N , N -dimethylaminophenyl and 4-nitrophenyl or 2,4-dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges connecting the electron-donor and the electron-acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The reverse solvatochromism was explained considering two resonance structures, benzenoid and dipolar forms. These compounds are good candidates for the investigation of the polarizability of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding.

Description: Laser flash photolysis-time-resolved infrared spectroscopy (LFP-TRIR) was performed on an acetonitrile or dichloromethane solution of triarylphosphines, Ar 3 P, in air. A transient spectrum consisting of several absorption bands appeared in the region of 1050–1300 cm −1 on the TRIR on a microsecond timescale, which disappeared on a millisecond timescale. To identify the observed transient intermediate , the IR spectra of possible intermediates of the photoreaction were simulated by theoretical calculations based on density functional theory (DFT). The IR spectrum simulated for the phosphine peroxidic radical cation, Ar 3 P + OO • , well predicted the observed IR spectrum, showing that Ar 3 P + OO • is formed as a transient intermediate upon the LFP of Ar 3 P in air. Copyright © 2014 John Wiley & Sons, Ltd. Laser flash photolysis-time-resolved IR spectroscopy (LFP-TRIR) was performed on an acetonitrile or dichloromethane solution of triarylphosphines, Ar 3 P, in air. A transient spectrum consisting of several absorption bands appeared in the region of 1050–1300 cm −1 on the TRIR on a microsecond timescale, which is identified to be the phosphine peroxidic radical cation, Ar 3 P + OO • , by comparison of the observed IR spectra with the spectra simulated based on the DFT calculations.

Description: Density functional theory method and B3LYP/6-311++G(d,p) level of theory were used to determine the acidity of alkyl sulfonic acids and polyolalkyl sulfonic acids in the gas and solution (H 2 O, DMSO, and CH 3 CN) phase. Polarized continuum model was applied to calculate p K a values of alkyl sulfonic acids and polyolalkyl sulfonic acids . A comparison between acidity of alkyl sulfonic acids and polyolalkyl sulfonic acids in the gas and solution phase indicates that the acidity strength of polyolalkyl sulfonic acids enhances with the increase of the cooperativity effect of intramolecular hydrogen bonds in polyolalkyl sulfonic acids . Natural bond orbital and quantum theory of atoms in molecules analyses also confirm the role of cooperativity effect on the acidity of polyolalkyl sulfonic acids . Copyright © 2014 John Wiley & Sons, Ltd. • The cooperativity effect of intramolecular hydrogen bonds in polyolalkyl sulfonic acids leads to an increase in the acidity strength in the gas phase and solution (H 2 O, DMSO, and CH 3 CN). • The electron density values for the first hydrogen bond in polyolalkyl sulfonic acids increase by addition of the number of hydroxyl groups. • Quantum theory of atoms in molecules calculations show that the intramolecular hydrogen bonds in polyolalkyl sulfonic acids are electrostatic (closed-shell) interaction in the nature.

Description: The aromatic nucleophilic substitution reaction of 3,6-dichloro-1,2,4,5-tetrazine (DCT) with a series of biothiols RSH: (cysteine, homocysteine, cysteinyl–glycine, N-acetylcysteine, and glutathione) is subjected to a kinetic investigation. The reactions are studied by following spectrophotometrically the disappearance of DCT at 370 nm. In the case of an excess of N-acetylcysteine and glutathione, clean pseudo first-order rate constants ( k obs1 ) are found. However, for cysteine, homocysteine and cysteinyl–glycine, two consecutive reactions are observed. The first one is the nucleophilic aromatic substitution of the chlorine by the sulfhydryl group of these biothiols (RSH) and the second one is the intramolecular and intermolecular nucleophilic aromatic substitutions of their alkylthio with the amine group of RSH to give the di-substituted compound. Therefore, in these cases, two pseudo first-order rate constants ( k obs1 and k obs2 , respectively) are found under biothiol excess. Plots of k obs1 versus free thiol concentration at constant pH are linear, with the slope ( k N ) independent of pH (from 6.8 to 7.4). The kinetic data analysis (Brønsted-type plot and activation parameters) is consistent with an addition–elimination mechanism with the nucleophilic attack as the rate-determining step. Copyright © 2014 John Wiley & Sons, Ltd. The title reaction is subjected to a kinetic investigation. We propose a bimolecular reaction type: addition–elimination (S N Ar) for the nucleophilic attack of the series of thiols to tetrazine, in which the formation of the Meisenheimer complex is the rate-determining step of the reaction. Subsequently, in some cases, a second intramolecular and intermolecular nucleophilic aromatic substitution of alkylthio with the amino group was evidenced.

Description: The Diels–Alder (DA) reaction is one of the most important reactions in organic chemistry. The controversy surrounding this reaction as to whether it follows a concerted or stepwise mechanism has existed for a long time. The reaction of 1,3-butadiene and ethylene is the paradigmatic example of the DA reaction. We have reinvestigated the mechanism of this reaction using density functional theory. The theoretical study considered all types of possible pathways for the reaction of 1,3-butadiene and ethylene using six functionals at different rungs of Jacob's ladder. Therefore, a complete picture is given for a thorough understanding of the iconic DA reaction, and a new stationary point during the reaction processes has been reported for the first time. The calculated results indicated that three functionals, ωB97X-D, M06-2X, and B2-PLYP, of the fourth and fifth rungs of Jacob's ladder performed well in the investigation of the mechanism of this reaction and that the reliable basis set should be larger than 6-311+G(2d,p). The cis -1,3-butadiene more easily reacted with ethylene compared with 1,3-butadiene in the trans conformation. The concerted mechanism was found to be energetically favorable, whose energy barrier is around 10 kcal/mol lower than that of the stepwise mechanism. Two investigated solvents, toluene and CH 3 CN, had little impact on this simple DA reaction. Copyright © 2014 John Wiley & Sons, Ltd. The reaction of 1,3-butadiene and ethylene is the paradigmatic example of the Diels–Alder reaction. Whether this reaction follows a concerted or stepwise mechanism has existed for a long time. We have reinvestigated all types of possible pathways of this reaction via density functional theory using six functionals at different rungs of Jacob's ladder. A complete picture is given for a thorough understanding of this iconic DA reaction.

Description: The catalytic hydrolysis of bis(4-nitrophenyl)phosphate (BNPP) and bis(2,4-dinitrophenyl)phosphate (BDNPP) catalyzed by α-nucleophiles in gemini micellar media was investigated at 27 °C. The cationic gemini surfactants, i.e., alkanediyl-α-ω-bis(hydroxyethylmethylhexadecylammonium bromide) (16- s -16 MEA 2Br − , where s  = 4 and 6) were used. Nucleophilic reactivity of α-nucleophiles such as hydroperoxide (HOO − ), acetohydroxamate (AHA − ), and butane 2,3-dione monoximate ions (BDMO − ) were compared. The kinetic rate data were treated by applying the pseudophase model. The cationic gemini surfactants show unusual rate acceleration toward the cleavage of phosphodiesters with nucleophiles. These studies reveal that the hydroperoxide ion shows the highest catalytic activity reported so far with an unprecedented acceleration rate, 10 7 times faster than that of the uncatalyzed reaction. The possible mechanism for the BNPP and BDNPP cleavage promoted by α-nucleophiles is proposed on the basis of kinetic analysis. Copyright © 2014 John Wiley & Sons, Ltd. In the present paper, we found that cationic gemini surfactants are excellent reaction media in combination with α-nucleophiles for phosphodiester hydrolysis, cleaving the P=O bond. The improvement of phosphate ester hydrolysis catalysis could be pursued by searching for both better-performing gemini surfactants and α-nucleophiles.

Description: The gas-phase acidity (GA) values were determined for a number of perfluoroalkyl-substituted sulfonylimides by measuring proton-transfer equilibria using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The GA scale below 286.5 kcal mol −1 for (CF 3 SO 2 ) 2 NH was extended and partially revised. The GA value of (C 4 F 9 SO 2 ) 2 NH which is currently the strongest acid was revised from 284.1 to 278.6 kcal mol −1 . The effect of fluorine atoms on the acidity of perfluoroalkyl-substituted sulfonylimides was described with the following model where N (α) , N (β) , N (γ) , and N (δ) are the numbers of fluorine atoms at α, β, γ, and δ position in R f SO 2 (R f  = perfluoroalkyl group), respectively. This correlation indicates that the electron-withdrawing ability of the R f SO 2 group can be described in terms of the number of fluorine atoms in the perfluoroalkyl group corrected by taking into account their positions. Copyright © 2014 John Wiley & Sons, Ltd. The gas-phase acidity scale below 286.5 kcal mol −1 has been extended and partially revised. A simple and accurate model is proposed for describing the gas-phase acidities of R f -substituted sulfonylimides.

Description: Density functional theory [B3LYP/6-311+G(d,p)] was used in combination with the conductor-like polarizable continuum model (CPCM) solvation model to investigate the relative stability and site-specific values of neutral and ionized tautomers of lumazine (LM) and 6-thienylLM (TLM). Two types of populations should be taken into consideration when calculating the , tautomers, and conformers. The major tautomer of neutral LM in aqueous solution is 13-LM (the 13 notation refers to the acidic protons being in positions 1 and 3 of LM) TLM has decreased acidity at N 8 relative to LM. Further, the trans conformer of TLM is more acidic than cis . Similar to the case of LM, for TLM, N 1 is more acidic than N 3 in the uracil part. However, N 8 is predicted to be a stronger acid than N 1 for TLM. This acidity enhancement is essentially because of a specific stabilization of the anion when the thienyl group replaces H. Two factors are responsible for the acidity strength of N 8 : The thienyl ring upon deprotonation acts inductively as an electron-withdrawing group, and the excess electron density is dispersed better when the system is trans and contains second-row atoms. Accurate pK a calculation requires that all conformers/tautomers be included into the calculation. Copyright © 2014 John Wiley & Sons, Ltd. Tautomerism and pK a : Lumazine (LM) and its 6-thienyl derivative (TLM) have been studied computationally. The tautomeric/conformer equilibrium dependence of the acid dissociation constant values of LM and TLM have been determined, with the prospective of designing new methodology of pK a calculations. It is important to include all the potential tautomers and rotamers during calculations of the pK a values.

Description: No abstract is available for this article.

Description: The degradation of azo dyes has attracted many research efforts not only due to the resulting environmental problems but also because the azo compounds with various substituents may show different degradation mechanism. It has been computationally found here, for the first time, that the HO• initiated cleavages of C–N and N–N bonds of alizarin yellow R with carboxyl group are kinetically competitive. In view of the formation of HO• adducts, the C–N and N–N bond cleavages of the hydrazone tautomer of alizarin yellow R are also kinetically competitive, but the former is more thermodynamically favorable. This result is different from that previously reported for the hydrozone tautomers of Acid Orange 7 and Acid Orange 8 containing hydroxyl and azo groups in neighboring positions, which are favorable to follow C–N bond cleavage mechanism both kinetically and thermodynamically. The decarboxylation occurs via an attack of HO• to the benzene ring carbon connecting to the carboxyl group rather than a direct attack of HO• to the carboxyl carbon atom. The anion form has higher reactivity than the neutral form in all of the reactions investigated. In addition, a water molecule as a proton relay reagent could significantly reduce the energy barrier for the N–N bond cleavage of alizarin yellow R. Copyright © 2014 John Wiley & Sons, Ltd. It has been computationally found that the HO• initiated cleavages of C–N and N–N bonds of alizarin yellow R with carboxyl group are kinetically competitive. The decarboxylation occurs via an attack of HO• to the benzene ring carbon connecting to the carboxyl group rather than a direct attack of HO• to the carboxyl carbon atom. A water molecule as a proton relay reagent could significantly reduce the energy barrier for the N–N bond cleavage of alizarin yellow R.

Description: 1 H and 13 C NMR studies and quantum chemical calculations show the interaction between 2,11-dithia-5,6,8,9-tetramethyl[3 2 ](1,4)cyclophane and nitrosonium cation to result in the formation of π- and n -complexes. According to DFT/B3LYP/6-31G(2d,p) calculations, formation of nitrosonium complexes is a strongly exothermic process both in gas phase and in SO 2 . Affinity of single-charged complexes to NO + is usually larger than that of double-charged and triple-charged complexes, affinity of all the charged complexes to nitrosonium cation in SO 2 being larger than that in gas phase. The π-complex with nitrosonium cation coordinated to the methylated aromatic ring is the most stable with structural characteristics being close to those obtained by X-ray diffraction for nitrosonium π-complexes of hexamethylbenzene and other arenes. The N―O bond lengths in all the complexes are quite close to each other and larger than that in NO + cation. The S―N bond length increases upon transition from single-charged to double-charged and polycharged complexes. Copyright © 2014 John Wiley & Sons, Ltd. 1 H and 13 C NMR studies show the interaction between 2,11-dithia-5,6,8,9-tetramethyl[3 2 ](1,4)cyclophane and nitrosonium cation to result in the formation of π- and n -complexes. According to DFT/B3LYP/6-31G(2d,p) calculations, formation of nitrosonium complexes is a strongly exothermic process both in gas phase and in SO 2 . The π-complex with nitrosonium cation coordinated to the methylated aromatic ring is the most stable. The first structural study of polycharged nitrosonium complexes is described.

Description: The solvent polarity parameter E T (30) is newly measured from the solvatochromism of the betaine dye for 84 solvents and re-measured for 186 additional ones. The results are organized in a database. It is shown that the validity of linear solvation energy relationships used for the determination of secondary E T (30) values is limited to non-hydrogen-bond donor solvents. Relationships with the chain length n are given for the determination of tertiary E T (30) values of the homologous H(CH 2 ) n Y solvent series. The parameter E T (30) is orthogonal to the function of the refractive index ( n 2  − 1) / (2 n 2 + 1). For non hydrogen-bond donor solvents, this allows to enter E T (30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright © 2014 John Wiley & Sons, Ltd. By means of solvatochromic betaine dyes, solvent polarity parameters E T (30) of 84 organic solvents are newly determined, and 186 are re-measured. Linear solvation energy relationships used for the determination of secondary values are shown to be strictly valid only for non-hydrogen-bond donor solvents. These findings allow the construction of a database of 270 reliable E T (30) values.

Description: Novel phthalimides ( ) possessing variability of cyclic amines have been synthesized and characterized by analytical and spectroscopic techniques. Phthalimide and crystallized in a triclinic system with space group P ī; however, an orthorhombic system with a chiral space group of P2 1 2 1 2 1 was observed for possessing piperidine cyclic amine. The hydrogen atoms attached to the central chiral carbon were oriented anti to each other resulting in minimum steric repulsion. The occurrence of C–H···O hydrogen bonds in enabled the building of several supramolecular structures. Hyperpolarizability 197.6096 Debye Å 2 calculated for was found to be higher than the hyperpolarizabilities, 138.0836 and 165.2521 Debye Å 2 measured for and , respectively. Subsequently, phthalimides ( ) were assessed for second harmonic generation (SHG) response, and a negligible response was recorded for and ; however, showed a significant response of 14.2 mV. In addition to acentric structure, helical structural motifs identified in could be responsible for its enhanced SHG response. Copyright © 2014 John Wiley & Sons, Ltd. Novel phthalimides have been synthesized, characterized and investigated for structural features and nonlinear optical applications.

Description: A novel asymmetrical diarylethene with a (formyloxyethoxy)ethyl-linked naphthalimide unit was synthesized, and its photochromic and fluorescence properties were systematically investigated in both solution and a PMMA film. The diarylethene showed significant photochromism and notable fluorescence switching properties upon irradiation with UV/Vis light. Compared with the parent diarylethene, introduction of the naphthalimide moiety was effective to increase the molar absorption coefficient, the fluorescence quantum yield, and fluorescent modulation efficiency of the diarylethene. This article is protected by copyright. All rights reserved.

Description: In the present paper, reaction of zinc-glycylphenylalanine ([Zn(II)-Gly-Phe] + ) with ninhydrin has been investigated in gemini (m- s -m type; m = 16, s  = 4–6) surfactants at temperature (70 °C) and pH (5.0). Monitoring the appearance of product at 400 nm was used to follow the kinetics, spectrophotometrically. The order of the reaction with respect to [Zn(II)-Gly-Phe] + was unity while with respect to [ninhydrin] was fractional. The reaction constants involved in the mechanism were obtained. In addition to the rate constant ( k Ψ ) increase and leveling-off regions are observed with the geminis, just like as seen with conventional surfactant hexadecyltrimethylammonium bromide (CTAB), the former produced a third region of increasing k Ψ at higher concentrations. A close agreement between observed and calculated rate constants was found under varying experimental conditions. A suitable mechanism consistent with the experimental findings has been proposed. Copyright © 2014 John Wiley & Sons, Ltd. Absorption spectra of the reaction product of [Zn(II)-Gly-Phe] + with ninhydrin in the absence and presence of geminis. The spectra of mixtures consisting the reactants in geminis exhibited the same maxima as that of aqueous solution. The spectra contain a broad peak at λ max (=400 nm). Although higher absorbance values were obtained in gemini micellar media. No shift in λ max was detected with surfactants, which indicates that the reaction product formed to be the same as in aqueous.

Description: Click chemistry is employed to couple two β-cyclodextrins at both ends of azobenzene moiety yielding dumbbell-shaped amphiphiles (AZO-β-CD dimer) constructed by rigid aromatic building blocks as “body”, and hydrophilic cyclodextrins as “head” with almost quantitative yield and purity. Bulk aggregates formed by the self-assembly of the supraamphiphiles through π–π stacking and hydrophobic effect are observed. Meanwhile, the rationally designed polyesters, named as AZO-PCL with controllable molecular weights and low polydispersities, are successfully synthesized by ring-opening polymerization of ε-caprolactone in the presence of p -aminoazobenzene as initiator. In the aqueous phase, very stable spherical particles are formed by host–guest interactions between AZO-β-CD and AZO-PCLs; the spherical aggregates inherit the photo-responsiveness of azobenzene. The detailed aggregation and disaggregation behaviors are fully investigated by TEM, SEM, NMR, 2D NOESY, IR, UV and XRD measurements. Compared to the previous works, our newly developed system can be fabricated with more readily manners, avoiding tedious synthetic process; the reversible and dynamic nature of the non-covalent interactions also can be modulated alternatively by UV or visible light. Thus, such dumbbell-shaped supra-amphiphiles are of great potential applications in the controlled delivery systems. Copyright © 2014 John Wiley & Sons, Ltd. Dumbbell-shaped amphiphiles (AZO-β-CD) were synthesized, and their aggregation behaviors demonstrated that π–π stacking is the driving force for the formation of the bulk-like aggregates, and also H-bonding is the synergistic operation of the force to maintain the aggregates into packed manner. In further study, stable spherical particles are formed by host–guest interactions between AZO-β-CDs and AZO-PCLs, and their self-assemblies are investigated. The results verified that such photo-responsive host–guest system is of potential applications in the controlled delivery systems.

Description: Calculations show that anomeric amides, amides bearing two electronegative atoms at the amide nitrogen, are unusual in structure and reactivity. They have much reduced amide resonance and also undergo the HERON reaction where anomeric destabilisation results in migration of one substituent from nitrogen to the carbonyl and formation of a resonance-stabilised nitrene. B3LYP/6-31G(d) calculations demonstrate how resonance and HERON reactivity are affected by bisalkoxyl substitution and aminoalkoxyl substitution at nitrogen. Because transition state structures for model reactions of N , N -dimethoxyacetamide and N -methoxy- N -dimethylaminoacetamide demonstrate complete loss of amide resonance, the overall barriers to their HERON reactions can be partitioned into a resonance (RE) and a rearrangement component ( E rearr ). REs for both amides have been calculated by isodesmic methods ( carbonyl substitution nitrogen atom replacement and a calibrated trans amidation method), and the reduction in total electronegativity at the amide nitrogen in N -methoxy- N -dimethylaminoacetamide results in an increase in amide resonance of about 4 kcal mol −1 relative to N , N -dimethoxyacetamide (RE of 8.6 kcal mol −1 ). However, there is a large decrease in E rearr by some 20 kcal mol −1 to 10 kcal mol −1 . Changes in these energies are rationalised on the basis of an increase in amide nitrogen lone pair energy, which increases resonance, and a higher energy substituent nitrogen lone pair enhancing the n N ―σ* NO anomeric effect and the ease of rearrangement . Intramolecular HERON reactions in twisted 1-aza-2-adamantanones, with no amide resonance, support the above variations in the rearrangement components to the activation barriers. On the strength of these findings, hydroxamic esters with only one oxygen at nitrogen will not undergo HERON reactions. Copyright © 2014 John Wiley & Sons, Ltd. B3LYP/6-31G(d) calculations with Y = NMe 2 instead of OMe increases resonance stabilisation by 4 kcal mol −1 but reduces E rearr for the HERON process by 20 kcal mol −1 . HERON reactions of model, fully twisted 1-aza-2-adamantanones support these changes in E rearr . Both effects are due to lower electronegativity of the amino N .

Description: A comparative analysis of the physicochemical properties of different donor–acceptor dyads, based on a perchlorotriphenylmethyl radical acceptor subunit linked through a vinylene π -bridge to ferrocene derivatives (1–3) or a tetrathiafulvalene (4) donor subunit, is presented. Intramolecular electron transfer and charge delocalization of these donor–acceptor dyads are discussed on the basis of data obtained in solution by cyclic voltammetry, UV–Vis near-infrared, and electron spin resonance spectroscopies. Bistability in the crystalline phase is also discussed on the basis of the results provided by X-ray diffraction analysis and temperature-dependent Mössbauer spectra. Copyright © 2014 John Wiley & Sons, Ltd. A comparative analysis of the physicochemical properties of different donor-acceptor dyads, based on a perchlorotriphenylmethyl radical acceptor subunit linked through a vinylene π-bridge to ferrocene derivatives or a tetrathiafulvalene donor subunit, is presented. Intramolecular electron transfer and charge delocalization of these donor-acceptor dyads are discussed on the basis of the data obtained in solution by different spectroscopic techniques. Bistability in the crystalline phase is also discussed on the basis of the results provided by X-ray diffraction analysis and temperature-dependent Mössbauer spectra.

Description: No abstract is available for this article.

Description: Rapid isomerization of pi-complex intermediates results in the formation of multiple isomers of alkyl aromatics during AlCl 3 -catalyzed reactions between linear olefins and aromatic rings. The authors present results of a kinetic study of reactions between p-xylene, 1-dodecene, and linear tetradecenes. Product distributions are well predicted based on a model of reversible pi-complex isomerization . Surprisingly, no double bond isomerization was observed in the linear olefins: All isomerization occurred in the pi-complexes. Copyright © 2014 John Wiley & Sons, Ltd. A kinetic model of rapidly isomerizing pi-complex intermediates explains the quantitative distribution of alkylate isomers observed during Friedel–Crafts reactions between p-xylene and linear olefins. Double bond isomerization was not observed in the olefins.

Description: No abstract is available for this article.

Description: The ability of an isolable N , N ′-diamidocarbene (DAC) to activate compounds containing early p-block elements was explored. At ambient temperature, the DAC formally inserted into the Si–H bonds of various silanes to afford the corresponding DAC–silane adducts. The aforementioned adducts did not undergo intramolecular ring expansion as observed with other carbene–silane analogues. The DAC was also found to form a coordination complex with aluminum chloride, and a structurally rich, tris(aluminum) species was obtained upon exposure of the DAC to trimethylaluminum. The results gleaned from these studies are expected to facilitate the development of novel organometallic species as well as of new types of organocatalyzed silylations and aluminations. Copyright © 2014 John Wiley & Sons, Ltd. Due to its attenuated nucleophilicity, a N , N′ -diamidocarbene (DAC) was found to activate only silanes that contained inductively withdrawing substituents and was unable to datively bind to tetrasubstituted silicon-containing compounds. In contrast, a Lewis adduct was obtained when the DAC was treated with aluminum chloride, and a novel organometallic complex containing three aluminum centers was afforded upon exposure to trimethylaluminum.

Description: Investigation of the relative reactivity of bonds in fullerenes will provide fundamental theory for the design of fullerene-based materials. We have theoretically investigated the reactivity of the Diels–Alder (DA) cycloaddition of cis -1,3-butadiene to all types of bonds in C 60 and C 70 using the M06-2X hybrid density functional theory (DFT) calculations ( J. Phys. Org. Chem . 2012, 25 850–855) and have pointed out that the DA cycloadditions of cis and trans forms of 1,3-butadiene to ethylene have a specially intimate relationship ( J. Phys. Org. Chem . 2014, 27 652–660). For the aim of telling a whole story of the DA cycloaddition concerning C 60 and C 70 , the DA cycloadditions of trans -1,3-butadiene to all types of bonds in C 60 and C 70 were explored at the same theoretical level as those of the cis -1,3-butadiene. The calculated results related with the trans - and cis -1,3-butadienes were compared. The potential energy curves of DA cycloadditions of trans - and cis -1,3-butadiene to C 60 and C 70 were discussed. The distortion–interaction energy model was employed to elucidate the origin of different reactivity of all kinds of C C bonds. The solvent effects were examined using the continuum solvent model. These current results, along with our previous research, will help to obtain an overall view of the DA cycloadditions of 1,3-butadiene to C 60 and C 70 . Copyright © 2014 John Wiley & Sons, Ltd. All possible types of Diels-Alder cycloadditions of trans -1,3-butadiene to C 60 and C 70 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 calculated results related with the trans -1,3-butadiene and cis -1,3-butadiene were compared. The present conclusion will help to obtain an overall view of the Diels-Alder cycloadditions of 1,3-butadiene to C 60 and C 70 .

Description: Theoretical investigation of the polarization effect on a potential single-molecule transistor has been studied with density functional theory. 4,4′-(2-Amino-5-nitro-1,4-phenylene)bis(ethyne-2,1-diyl) dibenzenethiol (AN-OPE), containing a donor and an acceptor (D–A) crossed to its oligo(p-phenylene-ethynylene) (OPE) backbone, was used as a prototype for this study. Simulation results indicate that AN-OPE has a higher on/off ratio on conductance than OPE because of the larger polarization along the D–A direction. This high on/off ratio was proved by the 20 times variation in molecular charge, 15 times variation in bond lengths, 49 times variation in polarizability, 9 times variation in the rotation angles, and 13 times variation in the highest occupied molecular orbital–lowest unoccupied molecular orbital gaps under the same gate using B3LYP/6-31G (d, p). And results imply that conjugated molecules with a cross D–A structure could be a good direction for constructing a better single-molecule field-effect transistor. Copyright © 2014 John Wiley & Sons, Ltd. 4,4′-(2-Amino-5-nitro-1,4-phenylene)bis(ethyne-2,1-diyl) dibenzenethiol (AN-OPE), containing a donor and an acceptor (D–A) crossed to its oligo(p-phenylene-ethynylene) (OPE) backbone, was designed as a potential single-molecule field-effect transistor (FET) and investigated with density functional theory. And results imply that conjugated molecules with a cross D–A structure could be a good direction for constructing potential single-molecule FET.

Description: This is a summary of the research of Charles L. Perrin and his coworkers in the areas of aromatic mercuration , vibronic borrowing, ipso factors in electrophilic aromatic substitution , malonic anhydrides, mechanisms of proton exchange in amides, stereoelectronic control, the so-called reverse anomeric effect, an NMR titration method for highly accurate measurement of relative acidities, secondary deuterium isotope effects on acidity, symmetry of hydrogen bonds in solution, and nucleophilic addition to a para -benzyne diradical, along with Perrin's contributions to teaching and to service. Copyright © 2014 John Wiley & Sons, Ltd. This is a summary of the research of Charles L. Perrin and his coworkers in the areas of aromatic mercuration, vibronic borrowing, ipso factors in electrophilic aromatic substitution, malonic anhydrides, mechanisms of proton exchange in amides, stereoelectronic control, the so-called reverse anomeric effect, an NMR titration method for highly accurate measurement of relative acidities, secondary deuterium isotope effects on acidity, symmetry of hydrogen bonds in solution, and nucleophilic addition to a para-benzyne diradical, along with Perrin's contributions to teaching and to service.

Description: No abstract is available for this article.

Description: High-level Density Functional Theory calculations, coupled with appropriate isodesmic reaction, are employed to investigate the effects of α-carbon, ammonium, phosphorus, and sulfur ylides, cyclization , and unsaturation on the stability, multiplicity, and reactivity of novel singlet (S) and triplet (T) carbenes. Among them the highly π -donating α -ammonium ylide is found to exert the highest stabilizing effect on the carbenic center. α -Ammonium ylides resist dimerization and hydrogenation . They show wider singlet–triplet energy gap (Δ Ε S–T ), broader band gap (Δ Ε HOMO–LUMO ), and higher nucleophilicity compared to the reported stable  N -heterocyclic carbenes. Aromatic cyclic unsaturated ammonium, phosphorus, and sulfur ylide carbenes appear more stable than their saturated cyclic analogs which are in turn more viable than their acyclic counterparts. Copyright © 2014 John Wiley & Sons, Ltd. Among 24  N -YHCs scrutinized, the cyclic unsaturated carbene with Y = NH 3 appears the most stable with a nucleophilicity more than the N -heterocyclic carbenes reported experimentally.

Description: A knowledge of the factors determining the magnitude of the bond dissociation enthalpy (BDE) is of importance to the advancement of theoretical organometallic chemistry and from the practical standpoint. The central atom and the substituents bound to it influence the BDE values; however, the interplay between the BDE and the substituent effects remains unknown. In this work, the literature data on substituent influence on the BDE of lithium, sodium, copper, silver, mercury, aluminium, gallium, silicon, germanium, tin, lead, phosphorus, antimonium, chromium, iron, cobalt, nickel, rhodium, and iridium compounds (37 series) have been analyzed, using the correlation analysis. Generally, the BDE values were first established to depend on the joint influence of the inductive, resonance, polarizability, and steric effects of substituents. The contribution of the polarizability effect ranges up to about 40%. Copyright © 2014 John Wiley & Sons, Ltd. The bond dissociation enthalpy values were first established to depend on the joint influence of the inductive, resonance, polarizability, and steric effects of substituents.

Description: The aromaticities of azines relative to benzene have been estimated by fusion with 15,16-dimethyldihydropyrene. Chemical shift data for the azine-fused dihydropyrenes (calculated at GIAO HF/6-31G*//B3LYP/6-31 + G*) were used to estimate the reduction in the dihydropyrene nucleus aromaticity. Choice of the saturated reference model was quite crucial in reliable estimation of aromaticity. Reference models with partial unsaturation at azine (21,23,25–32) gave better estimate of aromaticity than the parent dimethyldihydropyrene. Aromaticities of azines through chemical shift data and geometric parameter analysis were found to be 90–100% to that of benzene, highly consistent with the aromaticity estimation by nucleus independent chemical shift (0)πzz calculations. Copyright © 2014 John Wiley & Sons, Ltd. The aromaticities of azines are estimated to be comparable with those of benzene using the dimethyldihydropyrene probe. Magnetic and geometric parameters deliver similar results provided that a suitable non-aromatic reference model is chosen for 1H NMR analysis.

Description: No abstract is available for this article.

Description: A comprehensive analysis of solutions of 5-fluorouracil (5FU) in water and an organic medium (dimethylsulfoxide, DMSO) was carried out using quantum chemical methods and nuclear magnetic resonance (NMR) spectroscopy. The details of anionic form generation in the solution of 5FU with an equimolar amount of potassium hydroxide were studied by 13 С, 1 Н, 15 N and 19 F NMR. Interpretation of NMR spectral data was carried out using quantum chemical calculations at the TPSSTPSS/6-311+G(d,p) level of theory. Specific solvation of 5FU and 1THF-5FU was modeled in approximation using the five-water cluster model and solvate complex including two DMSO molecules. It was established that in an alkaline medium in DMSO 5FU occurred mainly as a type of an anion with a deprotonation on N(1) position of a pyrimidine ring whereas in water alkaline solution—as a mixture of two anions with a deprotonation on N(1) and N(3) positions with a predominant content of the latter form. For the quantitative definition of the deprotonation forms of 5FU the technique based on the data of theoretical and experimental NMR 13 C spectroscopy, tested on a model compound 1-(tetrahydrofuranyl-2)-5-fluoro-pyrimidinedione-2,4 (tegafur, THF-5FU), was offered. The N(3) anion was found from spectral data to be more thermodynamically stable than the N(1) anion by 2.40 kJ mol −1 (calculated value 2.24 kJ mol −1 ) in an alkaline–water solution. Both alkaline–water and alkaline–DMSO solutions of THF-5FU (THF-5FU/KOH = 1/1) were characterized by the ratio of the equilibrium concentrations of the anion and diketo-tautomer as 9:1 and 4.3:1, respectively. Copyright © 2014 John Wiley & Sons, Ltd. A comprehensive analysis of 5-fluorouracil and tegafur solutions in water and dimethylsulfoxide (DMSO) was carried out using theoretical and nuclear magnetic resonance methods. In DMSO, the anion is formed by proton separation from the nitrogen N(1) of 5-fluorouracil. In an alkaline–water medium, anions N(1) and N(3) existed in equilibrium, with a predominant content of the latter form. Both alkaline–water and alkaline–DMSO solutions of tegafur were characterized by the ratio of the equilibrium concentrations of the anion and diketo-tautomer as 9:1 and 4.3:1, respectively.

Description: The 1,3-dipolar cycloaddition (1,3-DPCA) reaction plays a crucial role during the functionalization of fullerenes, which have broad applications in the materials and pharmaceutical fields. In concert with previous experiments, we theoretically investigated the mechanisms of 1,3-DPCA of diphenyldiazomethane (DDMf) to two fullerenes (C 60 and C 70 ) using the M06-2X density functional method under vacuum and in solvents. To understand the influence of the dipolarophile on these reactions, the 1,3-DPCA of DDMf to three common acceptors, specifically tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and chloranil (CA), was also studied at the same computational level. The substituent effects on the five reactions were investigated by modeling 1,3-DPCA reactions with 12 different substituted DDMf (DDMs) with five dipolarophiles, totaling 60 reactions. Including the five unsubstituted DDMf reactions, 65 1,3-DPCA reactions were studied. The stereoselectivity, relative reactivity, solvent effects, and distortion/interaction energy model were carefully considered and analyzed based on their corresponding electronic structures, electrostatic potential surfaces, interaction models, solvent models, and thermodynamic data. An intermediate was identified for each of the 65 reactions. A possible biradical pathway for the reactions between DDMf and the two fullerenes was also investigated. The calculated results corroborate and enrich the experimental observations. The conclusion and detailed discussion are generally important for understanding the 1,3-DPCA reactions to fullerenes. Copyright © 2014 John Wiley & Sons, Ltd. We located one Int between the reactant and the TS for all 65 of the 1,3-DPCA reactions. We found that the distortion of the reactants toward their structures in the TS is a hindering factor, but the interaction energy promotes the reaction. We concluded that EDGs promote and EWGs hinder the five unsubstituted reactions.

Description: Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF 3 CF 2 CF 2 OCH 3 (HFE-347mcc3) with OH radicals and Cl atoms using M06-2X/6-31 + G(d,p) level of theory. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels, respectively. Using group-balanced isodesmic reactions, the standard enthalpies of formation for species are also reported. The calculated bond dissociation energy for C―H bond is in good agreement with previous data. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K. At 298 K, the calculated rate coefficients are in good agreement with the experimental results. The atmospheric life time of HFE-347mcc3 is estimated to be 4.4 years. Copyright © 2014 John Wiley & Sons, Ltd. The reaction kinetics of the H-atom abstraction reaction of CF 3 CF 2 CF 2 OCH 3 with OH radicals and Cl-atoms are investigated at M06-2X/6-31 + G(d,p) level of theory. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K.

Description: Hydrogen bond donor strength ( ) and acceptor strength ( ) have been successfully used in models of many environmental and chemical systems, and a number of computational methods have been developed to predict them. In this work, a quantum chemical Møller–Plesset perturbation (MP2) method is applied to estimate the binding free energies (Δ G hbond ) of several 1:1 hydrogen-bonded complexes. A correlation between the binding free energies and hydrogen bond strength is established. This relationship can be used to develop an accurate computational model for predicting and using binding free energies. The accuracy of the method in predicting Abraham (root mean squared deviation (RMSD) = 0.0693) and (RMSD = 0.0677) are comparable to the empirical, fragment-based ABSOLV method (RMSD = 0.1144 and 0.1281 for and , respectively). The binding free energy has been decomposed into its thermodynamic components, and it is demonstrated that the linear relationships in the dataset and the existence of magic point can be attributed to a constant entropy of reaction. Copyright © 2014 John Wiley & Sons, Ltd. Binding free energies of several donor-acceptor complexes were calculated using MP2 method. Similar to a previous analysis of experimental data, a magic point was observed when the binding free energies were plotted against the binding free energies of a reference donor or acceptor. On the basis of this observation, a computational model is presented to predict Abraham's hydrogen bond donor and acceptor strengths.

Description: Thirty-one samples of 3,4′/4,3′-disubstituted benzylideneanilines (XBAY) with specified UV–Vis absorption maximum wavelength (λ max ) were designed and synthesized by applying the equation (Eqn ) which was abstracted from the UV–Vis absorption maximum wavelength energy (ν max  = 1/λ max ) of 4,4′-disubstituted benzylideneanilines. Then, the UV–Vis data (λ max ) of the designed compounds were measured in anhydrous ethanol. The predicted UV–Vis data of designed compounds are in agreement with the experimental ones, in which the mean absolute error is 2.9 nm. The results show that Eqn is applicative for the prediction of UV–Vis absorption λ max values of both 4,4′-disubstituted benzylideneanilines and 3,4′/4,3′-disubstituted benzylideneanilines. For a same pair of groups (X and Y), one can at least get four disubstituted benzylideneaniline compounds which have different λ max values. It perhaps provides a convenient method to design an optical material for benzylideneaniline compounds. Copyright © 2014 John Wiley & Sons, Ltd. Thirty-one samples of 3,4′/4,3′-disubstituted benzylideneanilines with specified UV-Vis absorption maximum wavelength (λ max ) were designed and synthesized by applying the equation (Eqn (1)) which was abstracted from the UV-Vis absorption maximum wavelength energy (ν max  = 1/λ max ) of 4,4′-disubstitued benzylideneanilines. The experimental results show that Eqn (1) is applicative for the prediction of UV-Vis absorption λ max values of both 4,4′-disubstituted benzylideneanilines and 3,4′/4,3′-disubstituted benzylideneanilines.

Description: The type of specific intermolecular and interionic interactions that are established when an ionic liquid is dissolved in water was here analysed. The study of the solvatochromic response of dipolarity micro-sensors based on Reichardt E T (30) and Kamlet–Abboud–Taft solvent scales and the application of the solvent exchange model confirmed the formation of different intersolvent complexes in binary mixtures of (water + [C 4 mim] [BF 4 ]/[Br]) type. These complexes provide H-bond or electron pairs to the polar network, respectively. Moreover, for 4-methoxybenzenesulfonyl chloride hydrolysis reaction in the (water + [C 4 mim] [BF 4 ]) system, a higher inhibition (13 times) on the k obs values was observed. Multiple linear regression analysis that allows confirming the solvent effect upon the reactive system is due to the hydrogen-bond donor properties of intersolvent complex formed. Then, the correlation between two different solvent-dependent processes proved to be successful. Copyright © 2014 John Wiley & Sons, Ltd. From the analysis of dipolarity micro-sensors solvatochromic response and the application of solvent exchange model, we determine the tendency of the different components of binary mixtures formed by (W + ILs) to interact with potential solutes. Therefore, the analysis of correlation between the microscopic properties and k obs values for a hydrolysis reaction allows us to understand the chemical behaviour observed.

Description: Robert Burns Woodward is considered one of the greatest synthetic organic chemists of our time, if not the greatest. This article presents evidence that Woodward was also one of the greatest physical organic chemists as well. Among Woodward and his collaborators' most important accomplishments in the field of physical organic chemistry are: the Woodward–Hoffmann rules; the derivation and use of structure–mechanism–reactivity relationships in his multifold structure determinations and total syntheses; the Woodward ultraviolet rules and the Octant Rule; and his early demonstration that synthetic organic chemistry can contribute to the synthesis of potential superconductors and thus, to material science. Copyright © 2014 John Wiley & Sons, Ltd. While Robert Burns Woodward is considered one of the greatest synthetic organic chemists of the 20th century, if not greatest, this article presents evidence that Woodward was also one of the greatest physical organic chemists as well.

Description: Photodeoxygenation of dibenzothiophene S-oxide (DBTO) has been suggested as a clean way to generate atomic oxygen in solution. Sulfoxide bond dissociation enthalpies (BDEs) are important to the quantum yield and mechanism of this photodeoxygenation. In this study, BDE of substituted DBTO molecules with various functional groups were determined using M062X/aug-cc-pV(T + d)Z and MP2/aug-cc-pV(T + d)Z levels of theory. The sulfoxide BDE was determined using an isodesmic reaction. The observed effect of substitution was that functional groups with negative σ para values (electron donating) strengthen the sulfoxide bond and that substituents with positive σ para values (electron withdrawing) weaken the sulfoxide bond. The Mulliken charge on sulfur for DBTO and the corresponding dibenzothiophene were identified as a suitable indicator of the predicted S–O BDE. Moreover, steric and hydrogen bonding interactions were found to affect sulfoxide BDE for certain functional groups when located at the 1 or 4 positions of the substituted DBTO. Copyright © 2014 John Wiley & Sons, Ltd. The sulfoxide bond dissociation enthalpy (S–O BDE) of dibenzothiophene S-oxide (DBTO) derivatives was computationally determined. The observed substituent effects were an increase in S–O BDE for electron donating groups and weakening of the sulfoxide bond for electron withdrawing groups. Mulliken charges on sulfur were a suitable predictor of S–O BDE. Hydrogen bonding interactions and steric effects were observed and discussed for substituents in positions 1 and 4.

Description: Halogen bonding is the attractive interaction of an electrophilic region of a halogen with a nucleophile. Its geometry, energy, and dominantly electrostatic nature resemble that of the hydrogen bond. Halogen bond strength critically depends on the electron deficiency of the halogen. Accordingly, halonium ions that bear a formal positive charge are the strongest halogen bond donors known so far. Halonium ions, similar to H + , are capable of simultaneously interacting with two Lewis bases. The structure and properties of the resulting three-center halogen bonds are reviewed herein, based on their spectroscopic and computational data, with the emphasis being placed on one representative example, the [N–X−N] + interaction. The iodine and bromine-centered systems form symmetric three-center-four-electron halogen bonds that have comparable orbital and electrostatic contributions and a large extent of charge delocalization. Their formation yields significant stabilization. The [N–Cl–N] + bond is computationally predicted to resemble the symmetry of the three-center bond of the heavier halogens, whereas the fluorine-centered halogen bond is predicted to be asymmetric, and thus behave more similar to the analogous, asymmetric three-center [N−H−N] + hydrogen bond. Experimental confirmation of the latter predictions remains to be accomplished, along with studies of the possible influence of the disorder of the local environment on halogen bond symmetry, and investigations in the gaseous phase. The electronic structure and the geometry of three-center halogen bonds are of fundamental interest, and also of practical importance, for example due to the occurrence of three-centered halogen bonds in synthetic reagents. Copyright © 2014 John Wiley & Sons, Ltd. The halogen bond is a secondary interaction that is conceptually similar to the hydrogen bond. Three-center halogen bonds have so far received little attention, despite their unusual strength and exceptionally short bond lengths. The motion of the central halogen in such three-center bonds follows a single-well potential, in contrast to the double-well behavior of the hydrogen of analogous three-center hydrogen bonds.