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  • Physical Chemistry  (606)
  • Wiley-Blackwell  (606)
  • American Association for the Advancement of Science
  • Annual Reviews
  • 2005-2009
  • 1990-1994  (471)
  • 1980-1984  (135)
  • 1994  (239)
  • 1990  (232)
  • 1984  (135)
Collection
Keywords
Publisher
  • Wiley-Blackwell  (606)
  • American Association for the Advancement of Science
  • Annual Reviews
Years
  • 2005-2009
  • 1990-1994  (471)
  • 1980-1984  (135)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Structure and stability of 2σ/1σ* three-electron-bonded radical cations from 1,n-bis(alkylthio)alkanes in aqueous solutions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 17-22 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A large number of 1,n-bis(alkylthio)alkanes, R′S(CH2)nSR″, was investigated by pulse radiolysis in aqueous solutions. The sulphur-centred radical cations, which were obtained on oxidation of the dithia compounds by ·OH radicals, are stabilized via 2σ/1σ* three-electron interaction between two sulphur atoms. Intramolecular stabilization is the only process observed for n = 2-4, whereas for longer chain compounds with n 〉 4 some intermolecular sulphur-sulphur interaction is also indicated. The stability and yields of the three-electron-bonded species also depend on the nature of the substituents R′ and R″, and for the intermolecular systems are a function of solute concentration. The results corroborate earlier investigations and demonstrate, in particular, that the optical parameters are a very sensitive measure of changes in electron density and structure of the three-electron-bonded systems.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030105
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  • 2
    Electronic Resource
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    Solvolysis of highly reactive phosphorus-sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 23-34 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and mechanism of solvolysis of optically active tert-butylphenylphosphinothioic-O-trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030106
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  • 3
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    Stereochemistry of silver-ion-assisted solvolysis of tert-butylphenylphosphinothioic iodidate. Phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 35-37 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the stereochemistry of silver-ion-assisted solvolysis of a new optically active tert-butylphenylphosphinothioic iodidate demonstrated that the reaction proceeds with inversion of configuration at the phosphorus atom. Evidence for phosphathiacylium cation formation as a reactive intermediate is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030107
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  • 4
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    Probing of transient photoenol formation from ortho-methyl-substituted phenyl ketones by hydrogen-tritium exchange (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 38-40 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the photochemically induced hydrogen-tritium exchange in o-methyl-substituted phenyl ketones are reported. It is shown that the tritium exchange can be beneficial for probing transient photoenol formation, particularly when photochemical side-reactions are occurring.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030108
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  • 5
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    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030110
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  • 6
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    The kinetic deuterium isotope effect of proton-transfer reactions in solution. Comparison of the marcus and the quantum-statistical mechanical models (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 62-68 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free energy dependence of the kinetic deuterium isotope effect of proton-transfer reactions in solution is usually analysed in terms of the Marcus model. By means of modern computer techniques, the more general quantumstatistical mechanical model is also amenable to routine application. The differnces in the basic assumptions of the two approaches concerning the kinetic isotope effect are discussed. Reaction series for which both the Brønsted relation and the free-energy dependence of the kinetic isotope effect are available are analysed by means of the two models using one set of parameters for both free-energy relations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030112
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  • 7
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    Porphyrin-tyrosine interactions: Photo-CIDNP and NMR studies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 69-76 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strong 1H and 13C nuclear polarizations are observed when aqueous solutions of synthetic water-soluble porphyrins are irradiated in the presence of tyrosine and some of its derivatives. These polarizations are strongly pH dependent. Evidence is also shown for the formation, in the dark, of a complex between the reactants. The association constants are evaluated from the NMR chemical shifts on the aromatic tyrosine protons induced by the presence of the porphyrins. The nature of the intermediate radical pair generating the CIDNP effects is discussed. An electron-transfer reaction from tyrosine to the excited triplet state of the porphyrin, or within the porphyrin-tyrosine excited complex, is expected to be the primary step in the reaction. It is followed by subsequent proton transfer within the initial ion radical pair. The spin polarizations arise principally from the back-transfer step, as the reactants are the only products which are polarized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030202
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  • 8
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    Brønsted coefficients and the theory of acid-base catalysis of proton transfers from carbon acids (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 95-109 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model previously used to interpret proton transfers in ground and excited states and enzyme catalysis was applied to the general acid-base catalysis of carbon acids. The results are consistent with the predictions published for these systems and provide a new physical meaning for the Brønsted coefficients. It is shown that in addition to the linear free energy effect, the Brønsted coefficients are also influenced by the tightness of the transition states and by electronic effects. The model suggests that the increased reactivity of carbon acids towards proton transfer in non-hydrogen-bonding solvents is caused by an added electronic effect on the thermodynamics of the reactions. The curvatures of the Brønsted plots are interpreted in terms of an entropic contribution to the position of the transition state.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030206
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  • 9
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    Gas-phase nitration of thiophene and N-methylpyrrole by protonated alkyl nitrates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 110-118 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030207
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  • 10
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    Role of 2-carboxyl substituent in the tautomerization between two equivalent enol forms of 3-hydroxyphenalenone (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 485-488 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interconversion between two equivalent enol forms of 3-hydroxyphenalenone took place predominantly through a diketo form with a free energy of activation of ca 14 kcal mol-1 in DMSO solution determined by 125·8 MHz13C NMR measurement. On the other hand, the corresponding interconversion in 2-carboxy-3-hydroxyphenalenone was not frozen on the time scale of 13C NMR spectroscopy down to -60°C. This acceleration in the interconversion rate of the latter may be interpreted by a double proton switching between the hydrogen-bonded 2-carboxyl and 3-hydroxyenone moieties.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030712
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  • 11
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    Contribution of activity coefficients to the nucleophilicity of solvent components in solvent mixtures. Influence of added acetone on selectivity values, kE/kW, in ethanol-water mixtures (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 503-508 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Literature data on the change in the selectivity values, kE/kw, for several solvolysing systems in ethanol (E)-water (W) on addition of acetone were analysed. It is suggested that acetone acts as a basic cosolvent for both ethanol and water and that the change in the activity coefficients on changing the solvent composition is mainly responsible for the observed effect.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030804
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  • 12
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    Cross-interaction constants as a measure of the transition state structure. Part 8. Mechanism of the reaction of 2-phenylethyl benzenesulphonates with benzylamine in acetonitrile (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 545-549 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of reactions between 2-phenylethyl benzenesulphonates (2-PEB) and benzylamines in acetonitrile at 65·0°C have been studied; the mechanism was examined on the basis of the sign and magnitude of cross-interaction constants ρij and βij. In contrast to the reactions of 2-PEB with anilines in methanol, participation of the aryl-assisted pathway was negligible, with a strong indication that the reaction proceeds largely by an intermolecular SNi mechanism with a four-centre transition state (TS). The effect of substituents on the TS variation was in accord with the predictions of the quantum mechanical model.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030808
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  • 13
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    Solvent polarity scales. 1. Determination of ET and π* values for phosphonium and ammonium melts (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 534-544 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvent polarity of a series of organic salts in their molten state has been determined using the solvatochromic dyes: pyridinium N-phenolate betaine, the basis of the ET scale, and N,N-diethyl-4-nitroniline, one of the primary standards for the π* scale. Each of these dyes was dissolved in the following liquids: lithium acetate-sodium acetate-potassium acetate eutectic; ethylammonium chloride; dimethylammonium cloride; diethylammonium nitrate; ammonium trifluoracetate; tetraethylammonium acetate; tetrabutylphosphonium chloride; octyltributylphosphonium chloride; dodecyltributylphosphonium chloride; tetrabutylammonium bromide; tetrabutylphosphonium bromide; octyltributylphosphonium bromide; dodecyltributylphosphonium bromide; octyltributylphosphonium iodide; dodecyltributylphosphonium iodide; tetrahexylammonium benzoate; methyltrioctylphosphonium dimethylphosphate; and methyltrioctylammonium chloride. The ultraviolet and visible spectra were measured for each of these. In addition, data were collected as a function of temperature and in the presence of neutral and ionic additives. In general, these molten salts represent solvent polarities equivalent to moderately polar aprotic solvents such as acetone and acetonitrile. The salts with cations capable of being hydrogen bond donors gave considerably higher values, equivalent to or higher than water, the solvent with the highest value on the ET scale. These and the eutectic mixture are thought to involve specific dye-solvent interactions which cause these anomalously high values.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030807
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  • 14
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    Activation barriers in photosensitized pyrimidine dimer splitting (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 581-586 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pyrimidine dimers, which form by a symmetry allowed (πs2 + πs2) photocycloaddition reaction, are subject to photosensitized cycloreversion by electron donors, such as indoles. In a linked dimer-indole system, photoinitiated electron transfer occurs intramolecularly from indole to dimer to produce a charge-separated species (dimer-.-indole+.). This species undergoes cycloreversion in competition with back electron transfer. Studies of the temperature dependence and solvent dependence of this competition have allowed the relative values of the activation parameters for the competing processes to be determined. In water (5-65°C) the free energy of activation of splitting minus that of back electron transfer (ΔΔG≠ = ΔGspl≠ - ΔGbet≠) was found to be 1·3 kcal mol-1. The enthalpy of activation difference (ΔΔH≠) was found to be 1·1 kcal mol-1 and the entropy of activation difference (ΔΔS≠) was found to be -0·51 cal mol-1 K-1. In EPA (diethyl ether-isopentane-ethanol, 5:5:2; -85 to 25°C) the value of ΔΔG≠ remained the same, but the entropy and enthalpy contributions were different (ΔΔH≠ = 0·72 kcal mol-1; ΔΔS≠ = -1·8 cal mol-1 K-1). The results have been interpreted in terms of the effect of the polarity of the solvent on the transition states for the two competing processes. Enthalpy effects retard splitting more in water than in EPA, whereas entropy effects favor back electron transfer more in EPA than in water. Potential implications of these results for the mechanism of enzymatic photocycloreversion of pyrimidine dimers in DNA are considered.
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    URL: http://dx.doi.org/10.1002/poc.610030905
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  • 15
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031001
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  • 16
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    Stereochemistry and kinetics of addition of amines to acetylenic ketones (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 627-634 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of a series of 3-(p-substituted phenyl)-1-phenylprop-2-yn-1-ones with piperidine and morpholine in methanol were studied and their rates measured. The products were 3-piperidino- and 3-morpholino-3-(p-substituted phenyl)-1-phenylprop-2-en-1-ones. 1H NMR spectra were used to determine the configurations of the obtained products. A good Hammett correlation was obtained with ρ values of 1·15-1·10 and 1·15-0·53 for piperidine and morpholine, respectively, which suggest a carbanionic character of the transition state. A two-step mechanism is postulated for these nucleophilic additions.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031002
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  • 17
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    The spin delocalization substitutent parameter σJJ. 5. Correlation analysis of 19F chemical shifts of substituted trifluorostyrenes. The unresolved polar substituent parameter σmb (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 643-650 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 19F NMR spectra of 30 substituted α,β,β-trifluorostyrenes (Y-TFSs, 1) covering a diverse range of substituents are reported and discussed. Values (δF1, δF2, Δδ3 - 1 and Δδ3 - 2) derived from the 19F NMR chemical shifts of the fluorine atoms of 1 are found to correlate very well with σI and σR0. The results of the correlations of the 19F chemical shifts with dual (σF and σR) and triple parameter (σF, σR and σα) treatments are compared. An unresolved substituent parameter σmb, is proposed for applications to systems in which the substitutent Y interacts with a multiple bond and is compared with σ+.
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    URL: http://dx.doi.org/10.1002/poc.610031005
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  • 18
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    Direct measurement of the relative rates of C-protonation at unsubstituted and substituted α-and/or β-positions of a pyrrole ring (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 684-686 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct kinetic measurements of the C-protonation rates of 1,2,5-trimethyl- and 3,4-dimethyl-pyrroles allow the first comparison of the relative kinetic proton affinities of unsubstituted and substituted positions of the pyrrole ring.
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    URL: http://dx.doi.org/10.1002/poc.610031010
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  • 19
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    Stereospecificity in anionic 1, 1-addition to isocyanides. A re-examination of the (H- + HN≡C) potential energy surface (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 697-702 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The potential energy surface for the addition of the hydride ion to hydrogen isocynide reported previously was re-examined. An improved energy surface was explored at the MP2/6-31 + + G** level while relative energies were estimated at the MP4SDTQ/6-311 + + G** level and corrected for zero-point vibrational contributions. The calculated results show the existence of transition structures for both cis and trans-additions of H- to the carbon end of HN≡C even though the corresponding barrier heights are small. These transition structures did not exist at a lower level of theory (HF/4-31G) employed previously.The cis addition is calculated to be favoured over the trans addition by 10 kcal mol-1. The overall addition is thus strongly stereoselective, if not purely stereospecific. This result confirms our previous analysis of the stereoelectronic effect in the addition-elimination process involving imidoyl anions as intermediates. Recent experimental work on the addition of OH- to ArN≡C is discussed.
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    URL: http://dx.doi.org/10.1002/poc.610031102
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  • 20
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    Electrochemical reduction of substituted α,α,α-trifluoroacetophenones. Linear relationship between cyclic voltammetric peak potentials and Hammett substituent constants (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 723-731 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The peak potentials of substituted α,α,α-trifluoroacetophenones were measured in acetonitrile with 0·1 M tetrabutylammonium perchlorate. The cyclic voltammograms indicated an irreversible electrochemical process for the first wave (Epc1) and a partially reversible one for the second wave (Epc2) when the scan rate was slower than 100 mV s- 1. Excellent linear correlations were observed for Epc1 with σ constants (ρ = 0·526, r = 0·999) and for Epc2 with σ- constants (ρ = 0·605, r = 0·998), respectively. Therefore, unknown σ values such as -0·36 for 3, 4-ethyleneoxy can be estimated from these correlations. The mechanism of the electrode process probably involves a single electron transfer and the formation of a pinacol.
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    URL: http://dx.doi.org/10.1002/poc.610031105
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  • 21
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    Mechanism of formation of phosphonate carbanions with the use of a lithium salt and 1,8-diazabicyclo[5.4.0] undec-7-ene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 746-750 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The deprotonation reaction mechanism of methyl diethylphosphonoacetate in the presence of lithium salts and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was examined by infrared spectroscopy. It was found that the intermediate species formed by chelation of the bidentate phosphonate with a lithium cation or an ion pair of the salt deaggregated by DBU takes part in the reaction path. The role of the anion X- is to induce the elimination of a protonated DBUH+X- ion pair and that of the solvent is to compete with the bidentate phosphonate in cation solvation. A similar mechanism via a related intermediate is proposed to interpret the results obtained by other workers on the catalysis by Ba(OH)2 of the Wittig-Horner reaction.
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    URL: http://dx.doi.org/10.1002/poc.610031108
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  • 22
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    The current status of isomer enumeration of useful benzenoids and a new topological paradigm (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 765-783 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enumeration and development of conceptual tools for understanding the chemical properties of practical benzenoid hydrocarbons is stressed. Currently known isomer numbers for benzenoids having up to 60 carbons are summarized. Although there are well over 2 million isomers in this range, only approximately 500 benzenoid hydrocarbons have been characterized.
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    Reactions of molecules with two equivalent functional groups. 2. Acetylation of the isomers of bis(hydroxymethyl)benzene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 789-798 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The acetylation (with acetic anhydride-pyridine in tetrahydrofuran) of the ortho, meta and para isomers of bis(hydroxymethyl)benzene (1) was studied. Third-order rate constants k1 (formation of monoacetate 2 from 1) and k2 (formation of diacetate 3 from 2) for all three isomers were determined, as were the rate constants for acetylation of benzyl alcohol and its ortho- and para-ethyl derivatives under the same conditions. The compositions of the final product mixtures (comprising 1, 2 and 3) were ascertained as a function of the initial ratio of acetic anhydride to 1. Comparisons were made with predictions based on a previously published independent functional groups model, which assumes that k2/k1 = 0·50. All three isomers gave product mixtures whose compositions were in generally good agreement with predictions based on the model. For the para and meta isomers the ratios k2/k1 were determined experimentally to be 0·548 and 0·521, respectively. The k2/k1 ratio for the ortho isomer was found to be 0·605, and its k1 and k2 values were lower than those for the para and meta isomers. Possible explanations for the anomalous behavior of the ortho isomer are discussed.
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    Radical mechanism of nucleophilic substitution on halocyclohexane systems (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 812-816 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chlorocyclohexane does not react in the dark with diphenylphosphide ions in liquid ammonia, but it reacts under irradiation to give the substitution product. Bromocyclohexane reacts slowly in the dark, but this reaction is strongly accelerated by light, and inhibited by p-dinitrobenzene. 3-Bromo-2-tetrahydropyranyl allyl ether (used as a radical probe) reacts with diphenylphosphide ions under irradiation to give both the straightforward and the cyclized substitution products. This photostimulated reaction is also inhibited by p-dinitrobenzene. It is suggested that the chlro-bromocyclohexanes and related compounds react under irradiation by the SRN1 mechanism of nucleophilic substitution.
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    The influence of solvents on the basicity of dipolar amines (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 63-67 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative basicities of six monosubstituted dipolar trimethylamines (XCH2NMe2) were determined in nine different solvents from potentiometric titration. Solvation effects on basicity variations were analyzed by the solvatochromic parameters (π*, α and β). Non-specific solvation of the substituted dimethylammonium ions is not reflected adequately by the solvent's dipolarity-polarizability constant, π*. A better representation of non-specific interaction between solvents and the monosubstituted dipolar trimethylammonium ions is gained from the product of π* and the solvent dipole moment (μ). For these ions where the dipolar substituents are separated from the reaction center by one methylene unit, there is an interaction between the charge of the ammonium ion and the dipolar substituent. As a result, solvent molecules must not only solvate the dipolar substituents, but must also gain access between the lines of force of the dipolar substituent and the charge. Bulky solvents, such as nitrobenzene, cannot access adequately the region between the dipolar substituents and the reaction center to accomplish similar solvation as less bulky solvents.
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    Kinetic study of the formation and rupture of stable tetrahedral intermediates. C—O, C—N and C—S bond formation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 80-89 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Measured pseudo-first-order rate constants for intramolecular formation of tetrahedral intermediates from N-2-hydroxyethylphthalimide, N-2-aminoethylphthalimide and N-2-thioethylphthalimide at pH 〉 6 are reported. The reaction is specific and general base catalysed, with β(Brønsted) values 0·44, 0·52 and 0·52 respectively. From a plot of log kb (general base rate constants) vs γ′ [the affinities of EtXH (X = O, NH, S) toward the carbonylic carbon], β′nuc values of 0·01 (with OH- as specific base), 0·25 (with imdidazole as general base) and 0·27 (with HPO42- as general base were obtained). The observed relationships pxy = ϑβ′/ - ϑpKa = -ϑ(Brønsted)/ϑγ′ = 0·03 is supported by the predictions of an energy contour diagram, which, on extrapolation to a non-stable tetrahedral intermediate, predicts a late and slightly protonated transition state for the cleavage process. At pH 〈 3, these intermediates cleave to yield only the corresponding diacylimides. These reactions are general base and acid catalysed with β 〉 0·3 and α 〈 0·1. A fast equilibrium between the intermediate and its N-protonated (amide) form is reached. The general base rupture of the latter is faster than that of the corresponding non-protonated intermediate by a factor of ca 109 - 1010-fold.
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    Single-parameter versus dual-parameter correlation for radical reactions. Addition of bromine atoms to α-methylstyrenes (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 96-104 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A rigorous procedure was developed for measuring the relative rates of addition of bromine atoms to eleven substituted α-methylstyrenes (1-Y, with Y = CF3, NO2, F, CN, Cl, Br, CO2Me, Me, COMe, OMe and SMe). The reaction was run in tetrahydrofuran in the presence of HBr, O2 and dibutyl peroxyoxalate at 30°C. All products were derived from the YC6H4CMeCH2Br adduct radicals, which were immediately intercepted by O2. Correlation analysis of all the data confirmed the proposition that in the absence of measurable steric effects, the relative rates for radical additions can be correlated only by a dual-parameter equation and not by a single-parameter equation. Among various combinations of σ* and σx, the (σJJ* + σmb) combination yields the best correlation.
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    Methyl transfer from MeCo(III)Pc to thiophenoxide (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 90-95 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transfer of the cobalt-bound methyl in MeCo(III)Pc to thiophenoxide ion was studied (H2Pc is the planar macrocyclic phthalocyanine; the cobalt is held in the center in this plane). In dimethylacetamide solution, the reaction is rapid, requiring stopped flow for the kinetics, and yielding MeSPh and Co(I)Pc- in good yield. The kinetics are not simple second order, but instead approach a constant rate at high [PhS-], attributed to the reversible formation of an inert complex with PhS- occupying the vacant octahedral site in MeCo(III)Pc, on the other side of the phthalocyanine plane from the methyl group. The kinetics allow the estimation of the equilibrium constant, K, and the SN2 rate constant, k, which at 25°C have values of ca. 9·4 × 103 l mol-1 and 1·8 × 104 l mol-1, respectively. Although these values are rough, the ratio k/K is firm at 1·91 ± 0·02 s-1; this is the limit of the rate at high [PhS-]. An alternative mechanism, which is entirely consistent with the kinetics, involves a rate-determining homolysis of the Co—S bond of the same complex. The mechanism is not favored because the product yields are high for a radical combination process and alternative chain processes are kinetically unacceptable. Further, the rate constant is about what would be expected from the reactivity of other nucleophiles in SN2 reactions. Further arguments in favor of the SN2 mechanism are presented. This transfer of the methyl group from Co to S is part of the possible analogy to the vitamin B12-promoted methionine synthesis in nature. The other step in the biological, enzymatic process is the transfer of methyl from the nitrogen of N-methyltetrahydrofolate to cobalt. An attempt to model this with the very reactive N-methyl-2,6-dichloropyridinium ion was unsuccessful; the reaction took an entirely different course, presumably initiated by electron transfer, but leading to substantial loss of Cl- from the pyridine. No more than 0.5% methyl transfer took place. This system does mimic well the complete natural enzymatic process.
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    Announcements (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 116-116 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070209
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    URL: http://dx.doi.org/10.1002/poc.610070301
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    Protonation studies on isomeric tetrafluoro-2,11-dithia[3·3]cyclophanes, tetrafluoro[2·2]metaparacyclophane and their corresponding non-fluorinated analogs. Comparison with fluorinated and non-fluorinated[2·2]cyclophanes: A stable ion and semi-empirical (AM1, PM3) investigation (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 105-115 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Protonation of tetrafluoro-2,11-dithia [3·3]paracyclophane and tetrafluoro-2,11-dithia [3·3]metaparacyclophane in high-acidity super acid media, namely FSO3H.SbF5 (1:1) ‘magic acid’-SO2CIF, gave their corresponding acidic disulfonium ions. Additional ring protonation to give a disulfonium-monoarenium trication was not observed. With the non-fluorinated 2,11-dithia [3·3] cyclophanes, the disulfonium ions can be ring protonated in equilibrium to give a dynamic disulfonium-monoarenium trication. Tetrafluoro [2·2]-metaparacyclophane is monoprotonated at the meta ring and gives a complex mixture of conformational isomers. Multinuclear magnetic resonance data on the cyclophane precursors and their derived cations are compared and analysed. The energies, conformations and charge distributions of the isometric fluorinated and non-fluorinated [2·2] - and dithia [3·3] cyclophanes were calculated by the AM1 and PM3 methods, respectively. In all but one case the cyclophane arenium ions predicted by theory to be energetically most favoured are those observed in solution under stable ion conditions. In agreement with experiment, the instabilities of S,S,C-cyclophane trications are also theoretically predicted.
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    Announcement (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. I 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070302
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    Kinetics and mechanism of electron-transfer reaction of aquothallium(III) and coordinated thallium(III). Oxidation of metol with thallium(III) in acid perchlorate medium (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 117-121 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of oxidation of metol (N-methyl-p-aminophenol) by thallium(III) have been studied in a perchloric acid medium. This organic compound is employed extensively in photographic work. The stoichiometry of the reaction is represented by: C6H4(OH)NHCH3 + TIIII → C6H4(O)NCH3 + TII + 2H+The kinetics indicate the rate law: \documentclass{article}\pagestyle{empty}\begin{document}$$k' = \frac{{Kk\left[{metal} \right]}}{{1 + K\left[{metal} \right]}}$$\end{document} where k′ is the pseudo-first-order rate constant. The rate constants and thermodynamic parameters for the rate-limiting step have been evaluated.
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    The volume profile for a cheletropic reaction (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 178-180 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The volumes of activation and of reaction were measured for the reaction between sulphur dioxide and 2,3-dimethylbuta-1,3-diene to form 3,4-dimethylsulpholene. Values of ΔV and ΔV* are -33 and -35 cm3 mol-1, respectively in accordance with a concerted reaction having a very product-like transition state.
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    Secondary α-deuterium isotpe effect on the hydration of p-nitrobenzaldehyde (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 192-195 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The secondary α-deuterium isotpe effect on the equiliburium constant (KD/KH) for the hydration of p-nitrobenzaldehyde is 1·39 ± 0·05. The Kinetic secondary α-deuterium isotope effect (KD/KH) for the addition of water to p-nitrobenzaldehyde is 1·18 ± 0·07. This result demonstrates that there is extensive carbon-oxygen bond formation in the transition state for addition of water to the carbonyl group of p-nitrobezaldehyde.
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070501
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    Mechanism of the hydride transfer reaction of leuco crystal violet with cyanomethylene acceptors (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 218-220 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In the hydride transfer of Leuco Crystal Violet to form the Crystal Violet, cation, the role of cyanomethylene acceptors was found to be essentially different from that of p-benzoquinones, both previously believed to act as π-acceptors in the same manner.
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    Competition between decarboxylation and isomerization in the C3H5O2+ energy surface. Justification of the experimental results by molecular orbital calculations on the solvated ions (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 221-226 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In constrast with recent molecular orbital calculations on the decarboxylation of O-protonated 2-oxetanone, this experimental work indicates that no decarboxylation of this cation occurs in sulphuric acid solution up to 150°C, but instead a clean isomerization to protonated acrylic acid takes place. Parallel theoretical work shows that the gas-phase model is too crude to account successfully for the experimental facts obtained in acidic media. However, the latter are well reproduced when the effect of the solvent is taken into account. The present findings do not necessarily invalidate the reaction mechanism currently accepted to explain the rate enhancement and change of stereochemistry accompanying the decarboxylation of 3,4-disubstituted 2-oxetanones under acid catalysis.
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    Enolimine and geminaldiamine forms in the reaction of pyridoxal phosphate with ethylenediamine. An electrochemical and spectroscopic contribution (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 227-233 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The enol-keto tautomerism of the Schiff bases formed by pyridoxal 5'-phosphate (PLP) with ethylenediamine (Etd) and ethylamine (Et) was studied by electrochemical and spectrophotometric methods. The spectroscopic results revealed differences between the two reactions, i.e. the enolimine/ketoenamine ratio observed in PLP-Etd mixture is higher than that of PLP-Et. The differences observed in the electroreduction mechanism and stability of the Schiff bases formed provide additional evidence for an unusually high concentration of enolimine in PLP-Etd in buffered aqueous solutions.The results are consistent with a cyclic structure such as that previously proposed by Robitaille et al. [J. Am. Chem. Soc. 111, 3034-3047 (1989)] on the basis of spectroscopic data. Protonation of the terminal amino group of the Etd moiety in the Schiff base involves the formation of the cyclic species. The low basicity of ethylenediamine favours the formation of similar concentrations of the enol and keto tautomers of the Schiff base at neutral pH. This behaviour, also observed in the Schiff base formed by PLP and polylysine, may be involved in coenzyme-protein linkages.
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    Number and structure of solvolysis intermediates. Part 3.For Part 2, see Ref. 1.SN1 solvolysis of 2,2-Dimethyl-1-(p-Methoxyphenyl)Propyl p-Nitrobenzoate: Mechanism of the common ion salt effects arising at the stage of the second ion-pair intermediate (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 234-243 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2,2-Dimethyl-1-(p-methoxyphenyl)propyl p-nitrobenzoate (ROPNB) was subjected to solvolysis in phenol in the presence of tetrabutylammonium [carboxy-13C]-p-nitrobenzoate, in which the ‘common ion rate depression’ was confirmed to arise at the stage of the second ion-pair intermediate (Int-2). The unchanged substrate recovered at 46% reaction contained the isotopically labelled leaving group, indicating the occurrence of common ion exchange to the extent of 41-46%. In the solvolysis of the optically active substrate under identical conditions, the unchanged substrate was recovered with 51·4% racemization and ROPh was produced with slightly (1·56%) retained configuration, similarly to the solvolysis in the absence of the common ion salt. These isotope-tracer and stereochemical outcomes indicate that the common ion exchange in this solvolysis system should be attributable to the retentive nucleophilic attack on Int-2 by the common ion salt via a quadrupole (four-centre ion pair) transition state, accompanying the common ion rate depression, and they suggest that the special salt effect also should proceed by an analogous anion-exchange mechanism to that for the common ion effects.
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    Relative thermodynamic stabilities of the isomeric propenylbenzenes (1994)
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    Journal of Physical Organic Chemistry 7 (1994), S. 256-258 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The relative thermodynamic stabilities of 2-propenylbenzene (allylbenzene), and the E and Z forms of 1-propenylbenzene were determined over the temperature range 50-170°C by chemical equilibration in DMSO solution with t-BuOK as catalyst. The values of the thermodynamic parameters ΔG⊖, ΔH⊖ and ΔS⊖ at 298·15 K for each isomerization reaction between the title compounds were evaluated.
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    Hydride transfer reactions of Michler's hydride with different π-accetors (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 309-315 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydride transfer reactions of 4,4′-bis(dimethylaminophenyl)methane (Michler's hydride) with p-benzoquinones were studied. The rate of formation of Michler's Hydrol Blue was followed spectrophotometrically. The second-order rate constants and the activation parameters were estimated. The formation of a charge-transfer complex was observed at low temperatures. Stable and unstable paramagnetic species formed during the reactions were assigned by ESR spectroscopy. The observed kinetic behaviour and the stoichiometry were in line with those previously obtained for the systems involving Leuco Crystal Violet, Leuco Malachite Green and Leuco Bindschedler's Green. Hence the reaction is considered to proceed according to the so-far accepted multi-step mechanism. However, when tetracyano-p-quinodimethane or tetracyanoethylene was used as a π-acceptor, a comparatively stable radical ion pair was formed as a result of a one-electron transfer, followed by the gradual formation of Michler's Hydrol Blue. The kinetic behaviour and the stoichiometry of the reaction were examined, together with the enhanced kinetic effects of added triethylamine. A modified mechanism for these systems is proposed. The role of cyanomethylenes was found to be essentially different from that of p-benzoquinones, and therefore π-acceptors are divided into two groups of cyanomethylenes and p-benzoquinones.
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    Vinyl ether hydrolysis. 30. Effect of β-carboxy and β-carbomethoxy substitution (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 316-322 
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    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of hydrolysis of the vinyl ether functional groups of (Z)- and (E)-β-methoxyacrylic acid and (Z)-and (E)-β-methoxymethacrylic acid and their methyl esters were measured in aqueous perchloric acid solution. Additional rate measurements were also made for one substrate, (Z)-β-methoxymethacrylic acid, in buffer solutions down to pH 7, and a rate profile was constructed. The results show that the β-carboxy and β-carbomethoxy substituents produce strong rate retardations, ranging from 2000- to 25 000-fold, for both Z- and E-isomers in both the acrylic and methacrylic acid series. The rate profile for (Z)-β-methoxymethacrylic acid indicates that ionization of this substrate to the carboxylate ion form rises the rate of hydrolysis by a factor of 240. It is argued that this difference in reactivity of ionized and non-ionized forms of the substrate is due to conjugative and inductive effects of the substituents, rather than β-lactone formation as suggested in an earlier observation of the same phenomenon in a different system.
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070701
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    Editorial (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. ii 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1002/poc.610070702
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    Newer aspects of electron transfer in electrophilic Aromatic Nitration. Radical pairs as reactive intermediates by time-resolved spectroscopy (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 325-351 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aromatic nitration is effectively carried out by the deliberate irradiation of the charge-transfer absorption band (hvCT) of the transient electron donor-acceptor complex [ArH, NO2Y+], where NO2Y+ represents common nitrating agents. Time-resolved spectroscopy demonstrates that the charge-transfer nitration effected in this way proceeds via an electron-transfer mechanism, in which the collapse of the reactive triad, [ArH+ ·, NO2·, Y] is critical to the formation of the Wheland intermediate. Comparative product analyses of toluene and anisole nitrations together with the ‘non-conventional’ products arising from NO+ catalysis, ipso attack and addition/elimination show that the activation process leading to charge-transfer (photochemical) nitration is indistinguishable from that leading to electrophilic (thermal) aromatic nitration.
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    Stereochemistry and kinetics of methoxide ion substitution in (Z)- and (E)-O-methylbenzohydroximoyl cyanides (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 352-358 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and kinetics of the methoxide ion substitution reactions (Z)- and (E)-methylbenzohydroximoyl cyanidc [PhC(CN)=NOCH3] were investigated. The reaction of the (Z)-hydroximoyl cyanide with sodium methoxide in DMSO-methanol (9:1) solution at 44·8°C gives a mixture of methyl (Z)-O-methylbenzohydroximate [PhC(OCH3)=NOCH3] and the O-methyloxime of α-ketophenylacetamide PhC(CONH2)=NOCH3. The (E)-hydroximoyl cyanide undergoes methoxide ion-catalyzed isomerization to the E-isomer faster than it undergoes nucleophilic substitution. These observations were interpreted in terms of an addition-elimination mechanism in which the rate-limiting step is elimination of the nucleofuge (AN + DN#).
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    Kinetic studies on the aminolysis of 1-(trimethylsilyl)ethyl arenesulphonates in acetonitrile and methanol (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 359-363 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleophilic substitution reactions of 1-(trimethylsilyl)ethyl arenesulphonates with anilines and benzylamines in acetonitrile and methanol at 65·0°C were studied. The cross-interaction constants, ρXZ, between substituents in the nucleophile (X) and leaving group (Z) are relatively small (0·10 for XC6H4NH2 in MeCN) but similar to those for other SN2 processes at a secondary carbon atom. This provides further evidence for an approximately constant, loose SN2 transition state at a secondary carbon regardless of the size of the Cα substituent. The transition-state variations with substituents X and Z are in accord with that expected from the positive ρXZ value observed: a stronger nucleophile and/or nucleofuge leads to an earlier transition state, i.e. a lower degree of bond making and breaking.
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    Molecular mechanics calculations (MM3) on alkyl iodides (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 420-430 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 force field has been extended to cover alkyl iodides. Structures, vibrational spectra and heats of formation have been well fitted to available experimental data. The experimental and ab initio conformational relationships are also satisfactorily reproduced.
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    URL: http://dx.doi.org/10.1002/poc.610070806
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    Kinetics and mechanism of the imidazole-catalysed hydrolysis of substituted N-benzoylimidazoles (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 431-436 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Imidazole (Imz)-catalysed hydrolysis of benzoate esters proceeds via the intermediate formation of N-benzoylimidazoles. This paper considers the second step of this reaction, viz., Imz-catalysed hydrolysis of N-(4-X-benzoyl)imidazoles, X = CH3, H, Cl, CN and NO2, and N-(disubstituted benzoyl)imidazoles, 2-chloro-4-nitro, 2, 4-dinitro and 3,5-dinitro, in water-acetonitrile mixtures (10% or 14%, v/v, in organic solvent). On the basis of catalytic rate constants and the kinetic solvent isotope effect, it is shown that catalysis by Imz is of the general-base type. Unexpectedly, the hydrolysis of N-(2,4-dinitrobenzoyl)imidazole was found to be slower than that of N-(4-nitrobenzoyl)imidazole. It is shown that this reactivity order is due to a combination of a steric effect and stabilization of the reactant state due to a donor-acceptor interaction between the Imz moiety and the 2,4-dinitrophenyl ring.
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    URL: http://dx.doi.org/10.1002/poc.610070807
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    Micellar catalysis of organic reactions. Part 35. Kinetic determination of the critical micelle concentration of cationic micelles in the presence of additives (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 437-441 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method. This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations. Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic. Conventional methods cannot be applied with confidence to such systems. The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated. It was wound that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC. The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC. The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.
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    URL: http://dx.doi.org/10.1002/poc.610070808
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    Nucleophilic substitution reaction of benzyl bromide with N, N-Dimethylaniline: Significance of equilibrium cross-interaction constant (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 555-560 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic studies on the reversible reactions of benzyl bromides with N, N-dimethylanilines were carried out for both the forward (kf) and reverse (kr) directions. The equilibrium constants, K were calculated using the ratio kf/kr and the equilibrium cross-interaction constant, ρeXY was determined. The ρeXY value was shown to represent a maximum intensity of interactions between substituents X and Y through covalent bonds within a molecule. The normalized values of ρX (ρnuc) and ρXY indicate that in the transition state the fractional development or loss of polar and resonance interactions in the benzyl system are imbalanced or non-perfectly synchronized. In the forward reaction the fractional loss of resonance interaction becomes enhanced, whereas in the reverse reaction the fractional development of resonance interaction lags behind the corresponding changes of polar interactions by ca 45%.
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    URL: http://dx.doi.org/10.1002/poc.610071006
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    Competing solvolytic substitution and elimination reactions via a common irreversibly formed ion-molecule pair intermediate (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 578-584 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The acid-catalysed solvolysis of 9-(2-phenoxy-2-propyl)fluorene in mixtures of water with acetonitrile or methanol at 25°C provides 9-(2-hydroxy-2-propyl)fluorene, 9-(2-propenyl)fluorene, and 9-(2-acetamido-2-propyl)fluorene or 9-(2-methoxy-2-propyl)fluorene, respectively. The overall kinetic deuterium isotope effects for the reactions of the hexadeuterated analogue 9-(1,1,1,3,3,3-2H6)-9-(2-phenoxy-2-propyl)fluorene in 90 vol.% acetonitrile in water were measured as (kEH + kSH)/(kED6 + kSD6) = 1·54 ± 0·05, which is composed of the isotope effect kSH/kSD6 = 1·4 ± 0·1 for formation of the substitution products and kEH/kED6 = 4·0 ± 0·2 for production of 9-(2-methoxy-2-propyl)fluorene. Similar isotope effects were measured in other solvent mixtures. The results strongly indicate a branched mechanism involving rate-limiting formation of a common carbocation-molecule pair (with a secondary isotope effect of 1·54), which either undergoes nucleophilic attack by a solvent molecule (with a secondary isotope effect of ca 1), or is dehydronated (isotope effect ca 2·8) by the leaving group or by the solvent. The ion-molecule pair shows very low selectivities. Thus, in 50 vol.% acetonitrile in water, an acetonitrile molecule is as efficient as a water molecule as a nucleophile towards the ion-molecule pair, kMeCN/kHOH ≥ 1 (ratio of second-order rate constants). The discrimination between methanol and water is anomalously small, kMeOH/kHOH = 0·7.
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    Directional hydrogen bonding in the MM3 force field. I (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 591-609 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The MM3 molecular mechanics program calculates a fair representation of hydrogen bonding interactions, but to improve the MM3 hydrogen bond potential, a directional term has been added to the hydrogen bonding function. The resulting total function was reoptimized. Comparisons of the hydrogen bonding potential functions from ab initio, the original MM3, the current MM3(92) force field and the reoptimized MM3 force field MM3(94) for a variety of C,N,O systems are described.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610071103
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    Gas phase thermolysis of N-(tert-butylthio)allylamine and N-(tert-butylthio)diethylamine (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 585-590 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The title sulphenamides were pyrolysed in a stirred-flow reactor at temperatures of 310-410°C, pressures of 8-15 Torr and residence times of 0·4-2 s using toluene as the carrier gas. N-(tert-Butylthio)allylamine formed 73 ± 4% isobutene, 23 ± 3% propene and N-allylthiohydroxylamine. The first-order rate coefficients for the formation of isobutene and propene, respectively, followed the Arrhenius equations kC4(s-1) = 1012·52 ± 0·36 exp(-163 ± 5 kJ mol-1 RT) and kC3(s-1) = 1010·99 ± 0·29 exp(-151 ± 4 kJ mol-1 RT) N-(tert-Butylthio)diethylamine gave 97 ± 1% isobutene, 1·9 ± 0·4% isobutane and N,N-diethylthiohydroxylamine. The first-order rate coefficients for isobutene elimination followed the Arrhenius equation k(s-1) = 1013·45 ± 0·24 exp(-164 ± 3 kJ mol-1 RT). The formation of the products is interpreted in terms of an elimination reaction with a unimolecular, four-centered, cyclic transition state. The reactivity of these sulphenamides was found to be much higher than that of previously studied alkyl or aryl tert-butyl sulphides and disulphides.
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    Reactions of 1,3-dihaloadamantanes with diphenylphosphide ions by the SRN1 mechanism. Competition between intermolecular and intramolecular electron transfer reactions (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 610-614 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactivity of 1,3-dihaloadamantanes with diphenylphosphide ions (Ph2P-) in liquid ammonia was studied. 1,3-Dichloroadamantane (1a), 1-bromo-3-chloroadamantane (1b) and 1,3-dibromoadamantane (1c) reacted with Ph2P- ions under photostimulation by the SRN1 mechanism. Irradiation of 1c without Ph2P- ions gave no reaction (〈5%). Three products were found: 1,3-bis(diphenyphosphinyl)adamantane (2), (3-X-1-adamantyl)diphenylphosphine (X = Cl, 3a; X = Br, 3b) and 1-adamantyldiphenylphosphine (4). Compounds 2 and 4 were formed by intramolecular electron transfer (ET) of the radical anion 3a-· (3b-·); whereas 3a (3b) were formed by intermolecular ET of this radical anion to the substrates. It was observed that the product distribution depends on the substrate and reaction conditions.
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    URL: http://dx.doi.org/10.1002/poc.610071104
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    AB initio study of Diels-Alder reactions of 1,3,4-oxadiazole with ethylene, acrylonitrile, maleonitrile, fumaronitrile and 1,1-dicyanoethylene. Inverse order and ratio of endo/exo reactivity (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 634-640 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transition structures for the Diels-Alder reactions of 1,3,4-oxadiazole with ethylene, acrylonitrile, maleonitrile, fumaronitrile, and 1,1-dicyanoethylene were located with ab initio molecular orbital calculations with the RHF/3-21G theoretical model. The activation energies were calculated by single-point calculations with the RHF/6-31G* and MP2/6-31G* theory levels on the RHF/3-21G geometries. Geometries of two transition structures and the corresponding reactants were generated at the MP2/6-31G* and the energies evaluated at the MP3/6-31G* level. The values obtained are comparable to those generated by MP2/6-31G*//3-21G. The asynchronicity of the transition structures follow the same trend as the corresponding all-carbon Diels-Alder reactions with buta-1,3-diene and cyclopentadiene, but the activation energies are almost in opposite correlation. This behavior is explained by the oxadiazole nitrogen lone pair repulsion with the π-orbitals of the nitrile groups.
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    URL: http://dx.doi.org/10.1002/poc.610071108
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    Masthead (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610071201
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    Effect of cyclic acetal-type cationic surfactants on the basic dehydrobromination reaction (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 646-651 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of 2-(p-nitrophenyl)ethyl bromide with hydroxide ion was studied at 50 and 25°C in the presence of cationic chemodegradable surfactants, i.e. [2-alkyl(1,3-dioxolan-4-yl)methyl] trimethylammonium bromides Ia-c (alkyl: a = n-C9H19, b = n-C11H23, c = n-C13H27). The kinetic data were interpreted with the pseudo-phase ion-exchange (PIE) formalizm at both temperatures. The results indicate that the major source of rate enhancement is the increased reactant concentration in the small micellar reaction volume. The surfactant stability in micellar conditions was probed by means of a hydrolysis reaction of the surfactant 1,3-dioxolane ring. The kinetics of acid hydrolysis of Ia-c micelles, as a result of specific hydronium ion concentration, is one order of magnitude smaller than that of unaggregated systems.
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    URL: http://dx.doi.org/10.1002/poc.610071110
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    AB initio calculations of Diels-Alder transition structures for hetero-dienophile additions to cyclopentadiene (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 641-645 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transition states for the hetero-Diels-Alder addition of formaldehyde, formaldimine, diazene and nitrosyl hydride to cyclopentadiene were located with ab initio molecular orbital calculations. Asynchronous transition structures were located for the asymmetric hetero-dienophiles, whereas the symmetrical hetero-dienophile, cis-diazene, produced a synchronous transition structure. The relative reactivities are in good agreement with the LUMO energies of the hetero-dienophiles, and the transition states with the exo oxygen or nitrogen lone pairs have lower energies than the corresponding endo lone electron pair transition states. Endo/exo energy differences are much higher than in the addition of ethylene derivatives to cyclopentadiene.
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    Professor Robert W. Taft (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 655-656 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610071202
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    Equilibrium acidities and homolytic bond dissociation enthalpies of the acidic C—H bonds in dialkyl malonates and related compounds (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 751-756 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The equilibrium acidities, pKHA, of 18 dialkyl malonates, five alkyl 2-cyanoacetates and nine malononitriles and the oxidation potentials of their conjugate anions, EOX(A-), were measured in dimethyl sulfoxide solution. The homolytic bond dissociation enthalpies (BDEs) of their acidic C-H were estimated by combining their pKHA and EOX(A-) values. The pKHA values of the dialkyl malonates were found to increase from 15·9 to 16·4 to 18·4 as the dialkyl groups were changed from dimethyl to diethyl to di-tert-butyl, but the BDEs of the acidic C-H bonds remained constant [95·3±0·3 kcal mol-1] (1 kcal = 4·184 kJ). Introduction of methyl, ethyl, isopropyl and tert-butyl groups into the 2-position of diethyl malonate caused the equilibrium acidities to increase by 2·0, 2·4, 3·8 and 8·0 pKHA units, respectively, and the BDE values to decrease by 4·4, 3·7, 2·5 and 0·8 kcal mol-1, respectively. Introduction of a phenyl group into the 2-position of diethyl malonate had no effect on the acidity, but weakened the acidic C-H bond by 10 kcal mol-1. The effects on acidity and BDE of introducing 3,4,5- (MeO)3C6H2CO, CF3, Me3N+, c-C5H10N, p-MeC6H4, p-NO2C6H4, PhO, F and c-C5H5N+ groups into the 2-position of diethyl malonate were also examined.
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    Study of the hydrogen bond donor acidity of binary aqueous mixtures and their role in reversed-phase liquid chromatography (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 757-769 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvatochromic hydrogen bond donor (HBD) acidity parameter (αmix) of aqueous mixtures of methanol, acetonitrile, propan-2-ol and tetrahydrofuran were determined spectrophotometrically. The study was carried out at 25deg;C as a function of composition. The indicators used were 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate, 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)phenolate and Fe(LL)2(CN)2 (LL = N-(2-pyridylbenzylidene)-3,4-dimethylaniline). The HBD acidity of the aqueous organic mixtures was related to retention in reversed-phase liquid chromatography.
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030501
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    β-Secondary deuterium isotope effect and solvent isotope effects in catalysis by subtilisin BPN′ (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 260-265 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Subtilisin BPN′ catalyzes the hydrolysis in protium and deuterium oxides of p-NO2C6H4OCOCL2NHCO2CH2C6H5(L = H, D) in the pH(D) range 5·0-8·5 (H2O) and 5·4-9·0 (D2O), according to simple Michaelis-Menten kinetics. The parameter kcat/Km exhibits pH(D) inflection points of 7·17 ± 0·05 (H2O) and 7·69 ± 0·08 (D2O), and kcat shows 6·88 ± 0·05 (H2O) and 7·50 ± 0·07 (D2O). The ‘normal’ ΔpK values of 0·5-0·6 indicate no unusual effects of D2O on enzyme properties. The solvent isotope effects (H2O/D2O) on the limiting values of the rate constants at high pH(D) are 1·13 ± 0·07 for kcat/Km and 1·29 ± 0·05 for Kcat. These small effects indicate no more than minor contributions of general acid-base catalysis for rate-limiting events for either kcat/Km or kcat. The β-deuterium secondary isotope effects (2H/2D) are roughly estimated by extrapolation as 0·95 ± 0·01 for kcat/Km, corresponding to substantial tetrahedral character in the transition state, and 1·03 ± 0·03 for kcat, consistent with no tetrahedral character. Models consistent with these results have as rate-limiting events for kcat/Km nucleophilic attack by active-site imidazole and for kcat, among other possibilities, the release of carboxylate product from the imidazolium form of the enzyme.
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    Theoretical studies on the gas-phase pyrolysis of acetic anhydride and diacetyl sulphideDetermination of Reactivity by MO Theory, Part 61. For Part 60, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 279-284 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase thermal decomposition of diacetyl compounds, (CH3CO)2X with X = O and S, was investigated theoretically using the semiempirical MO methods MNDO and AM1. The initial decomposition of the diacetyl compounds proceeded through a six-membered ring transition state involving the keto form with a slightly lower activation enthalpy for diacetyl sulphide (X = S); the process via an enolic form of the transition state was kinetically unfavourable. In the initial decomposition of the diacetyl compounds and in the subsequent pyrolysis of acetic and thioacetic acid, ketene formation was found to be the most preferred path, where the ease of Cα—X bond cleavage is relatively more important than nucleophilic attack on the β-hydrogen in determining the overall reactivity. In the methane formation process, the reactivity was entirely dependent on the X—H bond strength in CH3COXH where X = S, NH and O.
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    Inhibition of peroxidations of lipids and membranes by estrogens (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 309-315 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The antioxidant activity of 2-hydroxyestradiol was measured quantitatively and compared with those of other estrogens in oxidations of methyl linoleate in homogeneous solution and in aqueous dispersions, oxidations of soybean phosphatidylcholine liposomal membranes and oxidative haemolysis of rabbit erythrocytes, all induced by free radicals generated from a radical initiator. Similar antioxidant activities of estrogens were observed, irrespective of the oxidation system. 2-Hydroxyestradiol was found to be a potent radical scavenger and its antioxidant activity was close to that of α-tocopherol, the strongest natural antioxidant. Other phenolic estrogens such as estrone, estriol and β-estradiol showed a modest antioxidant activity and testosterone did not act as an antioxidant.
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    Cycloadditions of 2-diazopropane to bicyclo[2.2.1]hept-2-enes. Direct experimental evidence for an asynchronous mechanism (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 339-345 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Diazopropane, generated by photolysis of 2-methoxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline, was trapped in situ by cycloaddition to norbornene, endo- and exo-5-methylnorbornene, endo- and exo-5-phenylnorbornene, endo- and exo-5-methoxycarbonyl norbornene and endo- and exo-dicyclopentadiene. In all cases, only exo addition was observed. In spite of the exo approach of diazopropane to the norbornene double bond, endo substituents at C-5 and/or C-6 influenced the regiochemistry of addition whereas exo substituents did not. The results are interpreted in terms of a concerted, asynchronous mechanism in which C—C bond formation runs well ahead of N—C bond formation, as predicted from theory. The regiochemical control exercised by apparently remote endo substituents provides a new experimental criterion for asynchrony or synchrony of cycloadditions that are known to be concerted.
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    Gas-phase acidities of acrolein and methyl acrylate (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 346-348 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase acidities of acrolein and methyl acrylate were measured by bracketing in a flowing afterglow/SIFT apparatus. For acrolein ΔG°acid = 369 ± 4 kcal mol-1 and for methyl acrylate ΔG°acid = 373 ± 4 kcal mol-1. These acidities are substantially lower than those of the saturated analogs propionaldehyde and methyl acetate, respectively, even though hydrogens attached to sp2-hybridized carbon are intrinsically more acidic than those attached to sp3-hybridized carbon. Resonance stabilization of the neutral form by conjugation of the C=C double bond with the carbonyl group and allenic destabilization of the anionic form of the two acids can account for the relatively low acidities.
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    A study of a novel degenerate carbocation rearrangement of the 4,9-dimethyl-9-barbaralyl cation by dynamic 13C and 1H NMR spectroscopy in superacid (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 349-357 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 4,9-dimethyltricyclo [3.3.1.02,8]nona-3,6-dien-9-yl (4,9-dimethyl-9-barbaralyl) cation (3) was generated from 4,9-dimethyl-9-barbaralol (5) at -135°C in two different superacid mixtures [FSO3H—SO2CIF—SO2F2(1:6:1) and FSO3H—SO2CIF—SO2F2—CHCl2 (2:10:10:1 by volume)]. Its 1H and 13CNMR spectra show a strong temperature dependence in the range -150 to -125°C. The changes in band shapes with temperature show that the following exchanges take place: 4-methyl with 9-methyl, C-4 with C-9, C-1 with C-3 and C-2 with C-8. C-5, C-6 and C-7 are found not to exchange rapidly either with each other or with the other carbons in 3. The mechanism of this novel rearrangement is suggested to involve the bicyclic 2,7-dimethylbicyclo [3.2.2] nona-3,6,8-trienyl cation and the secondary barbaralyl cation 4,6-dimethyltricyclo [3.3.1.02,8] nona-3,6-dien-9-yl as intermediates rather than 7,8-dimethyl bicyclo [3.2.2] nona-3,6,8-trienyl cation, which does not have a methyl group on the allyl cation moiety. Comparisons with rearrangement mechanisms for other barbaralyl cations were also made. The rate constant for the degenerate rearrangement of 3 is 160 s-1 at -140°C, which corresponds to ΔG≠s = 26 kJ mol-1 (6·3 kcal mol-1). At -125°C ion 3 rearranges non-degenerately to the 1,4-bishomotropylium cation 1,8-dimethylbicyclo [4·3·0] nona, 2,4,7-trienyl (4) with k = 3 × 10-4 s-1. A mechanism for this rearrangement and the synthesis and purification of the ion precursor 4 are also reported.
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    Dephosphorylation by peroxyanions in micelles and microemulsions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 390-396 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dephosphorylation of p-nitrophenyl diphenylphosphate (pNPDPP) by OH- in aqueous cationic micelles of cetyltrimethylammonium hydroxide (CTAOH) is inhibited by tert-butyl hydroperoxide (t-BuO2H), which reduces the binding of OH-, and whose anion is a relatively ineffective nucleophile. Reaction is faster in microemulsions of CTACl, n-octane and OH-, with t-BuO2H as cosurfactant, than in otherwise similar microemulsions with t-butyl alcohol as cosurfactant. Dephosphorylation by m-chloroperoxybenzoate ion is slower in microemulsions of cetyltrimethylammonium mesylate or benzenesulfonate, with n-octane and tert-butyl alcohol, than in cationic micelles, but a wide range of concentrations can be examined. The reaction rates qualitatively follow the concentration of peroxy acid relative to surfactant, and inert anions slow the reaction. Dephosphorylation by peroxyphthalate dianion in micelles of CTACl fits a pseudophase kinetic model, except in very dilute surfactant where reaction is faster than predicted.
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    Synthesis and spectroscopic properties of stereoisomeric 5,7-oxido-6-hydroxyiminocholestane derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 404-413 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The four possible diastereomeric 5,7-oxido-6-hydroxyiminocholestanes and their O-acetates have been synthesized. The stereochemistry of one of the latter has been proved unequivocally by x-ray diffraction. Their 1H and 13C NMR and also their circular dichroism spectra are discussed. It is now also possible to determine unequivocally the stereochemistry of the ring-junction geometry and the oxime E or Z stereochemistry.
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    Role of exciplex and ion pair in the photosensitized oxygenation of 1,4-diphenyl-1,3-butadiene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 509-518 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 9,10-Dicyanoanthracene (DCA) sensitized the photooxygenation of 1,4-diphenyl-1,3-butadiene(1a) and its 4,4′-dimethoxy derivative (1b) to afford the corresponding endoperoxides 2 and the other oxidized products such as aldehydes and epoxides. The mechanism of the DCA-sensitized photooxygenation of 1 was diversified by solvent polarity. In non-polar solvents the reaction involves an exciplex intermediate, which leads to formation of triplet DCA (3DCA*) with an efficiency of 0·64 in the case of 1a. The resulting 3DCA* acts as a sensitizer for the generation of singlet oxygen (1O2) and thus 1O2 reaction occurs exclusively to give 2. On the other hand, single electron-transfer quenching of 1DCA* by 1 is feasible in polar acetonitrile and a primary ion pair can be formed. Competing with fast back electron-transfer deactivation, the primary ion pair produces free ions in limited yield to furnish electron transfer oxygenation. In the case of the DCA-1a system, free ions were produced with an efficiency of ca 4%. Thus, in acetonitrile, electron-transfer oxygenation partly took place to give the other oxidized products, whereas the 1O2 pathway was still valid and responsible for the formation of 2. The effect of solvent polarity was apparently less pronounced in the case of 1b because the reactivity of 1b toward 1O2 is about five times higher than tht of 1a. For such 1O2-reactive substrates, the electron-transfer pathway would become dominant only when the substrate concentration is impractically high.
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    Cross-interaction constants as a measure of the transition state structure. Part 9. The degree of bond formation in the SN2 transition state involving anionic nucleophiles (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 550-554 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The second-order rate constants of the reactions between benzenesulphonyl chlorides and anionic nucleophiles, benzoates and cinnamates, in methanol at 30·0°C are reported. A marked increase in rate found with a p-nitro substituent in the substrate indicated the development of an electron-rich centre on the S atom in the transition state. The two types of cross-interaction constants, ρxy and λxy, suggested that bond formation in the SN2 transition state with anionic nucleophiles is greater than that for the corresponding reaction with aniline nucleophiles.
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    Synthesis and chemistry of azolenines.The term ‘azolenines’ refers to the non-aromatic isomers of the azoles. Part 19.For Part 18, see Ref. 1. Basicities of some 2H- and 3H-pyrroles and the remarkably large pKa′ of 2,2,3,5-tetramethyl-2H-pyrrole (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 555-557 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: pKa′ Values are reported for two 2H-pyrroles and their 3H-pyrrole isomers. The latter have basicities of the same order as similarly substituted pyridines, whereas the former are 2-2·5 pK units more basic, 2,2,3,5-tetramethyl-2H-pyrrole having a pKa′ of 8·40, close to that for 2-aminoimidazole. Possible reasons are given.
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    A valence and charge criterion for reactivity of π electron systems (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 599-605 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new criterion for the reactivity of π electron systems is proposed. The method incorporates and modifies ideas of Coulson and Fukui et al. about free valence. The proposed reactivity index includes covalent and lonic components and is suitable for elctrophilic, radical and nucleophillic attack. The method is tested for a few simple π systems and differences from Coulson and Fukui et al. are discussed. Finally, it is applied to the electrophilic attack of a series of substituted benzenes and to nucleophilic attack of a series of subsituted benzoic acid esters.
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    Ionization constants of 5-pyridylmethylenehydantoins in 80% (w/w) dimethyl sulphoxide-water at 25 °C (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 703-710 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ionization constants of nine amphoteric 5-pyridylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide-water at 25 °C. The effects of structure and Z/E configuration on both pKaI and pKaII values are discussed. The especially low basicity and acidity of the Z-isomers of the N-unsubstituted and 3-methyl-substituted 5-(2-pyridylmethylene)hydantoin are attributed to the formation of intramolecular N(1)—H…N hydrogen bond in the s-cis conformation of these compounds. The existence of N(1)—CH3…N attraction is also postulated for the Z-isomer of 1-methyl-5-(2-pyridylmethylene)hydantoin.
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    Heats of formation of organic molecules by ab initio calculations. 1. Aliphatic amines (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 732-736 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A bond energy scheme has been developed and two previously existing schemes have been extended for the calculation of heats of formation of aliphatic amines using ab initio 6-31G* energies in place of experimental data. The results are in good agreement with those obtained experimentally and suggest that this method can be used to predict heats of formation of molecules of this class with an accuracy competitive with good quality experiments, and with probable errors of less than 1 kcal mol-1.
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    MO study of the possibility of a concerted mechanism in the pinacol rearrangement (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 737-745 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ab initio SCF-MO method was employed to examine the possibility of a reaction pathway without a carbocation intermediate in the pinacol rearrangement. The molecular geometries of the transition states were obtained for the 1,2-hydride shift together with H2O elimination, starting from the various methyl-substituted protonated 1,2-diols. It was found that the activation energies depend strongly on the substitutents. A comparison of the relative energies between β-hydroxycarbonium ions and the transition states of the concerted mechanism suggests that the stepwise mechanism is less favourable than the concerted path in each case.
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    Cross interaction constants as a measure of the transition state structure. 13. Steric effects of the N,N-dimethyl group on the transition state structure in aminolysis of alkyl benzenesulphonates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 751-756 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic studies on the reactions of methyl (MBS) and ethyl benzenesulphonates (EBS) with N,N-dimethylanilines (DMA) in methanol and acetonitrile are reported. The cross interaction constants ρXZ and βXZ, between the substituents in the nucleophile (X) and the leaving group (Z) indicated that the transition states (TS) are looser than those for the reactions with anilines, but the relative tightness between the two substrates was the same; the TS was tighter for EBS despite the increase in steric effect leading to looser TSs for MBS and EBS alike. The TS variation between two different reaction series expected from the simple Hammett and Brønsted coefficients, ρX, ρZ, βX and βZ, was incompatible with that predicted by the cross interaction constants, demonstrating again the unreliability of the simple parameters.
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    Microenvironmental effects in solid-state reactions. Dispersive kinetics of conformation-dependent charge delocalization in aliphatic diamine radical cations (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 757-759 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of conformation-dependent charge delocalization in radical cations generated from a series of α,ω-diaminoalkanes, (CH3)2N(CH2)nN(CH3)2, (n = 1-3) in a 3-methylpentane glassy solution at 90 K are discussed in terms of dispersive kinetics with the use of the time-dependent rate constant in the form k(t) = Btα - 1. It was found that the activation energy distribution function became broader as the number of methylene groups separating the two nitrogen atoms increased, and that this process was accompanied by a substantial increase in the mean value of the activation energy.
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    Absolute hardness and aromaticity: MNDO study of benzenoid hydrocarbons (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 784-788 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Absolute hardness calculated by the MNDO method has been shown to be a good measure of aromaticity for 14 benzenoid hydrocarbons. Comparisons among hardnesses at different levels of approximation are given. The parallelism of the aromaticity and hardness concepts in benzenoids is elaborated.
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    Negligible kinetic solvent interactions for the rate of photobromination of toluenes where the bromine atom is a principal chain carrierDedicated to Professor Ikchoon Lee on the occasion of his 60th birthday. Preliminary results of this work have been presented earlier. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 803-806 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The bromine atom is a major chain carrier in the photobromination of toluenes by N-bromosuccinimide. Only an uncomplexed bromine atom can abstract hydrogen atoms from toluenes. The nature of the polar transition state is entirely different from that of solvolytic reactions and the solvent polarity therefore cannot infuence the rates of the bromination.
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    Mechanisms of acylation of 2,3-dihydrobenzoxazol-2-one and 2H-1,4-benzoxazin-3(4H)-one (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 807-811 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the acylation of 2,3-dihydrobenzoxazol-2-one with dodecanoic acid in polyphosphoric acid were investigated. Two competitive reactions occurred at the 3- and 6-positions. The acylation reactions in polyphosphoric acid of 2,3-dihydrobenzoxazol-2-one and 2H-1,4-benzoxazin-3(4H)-one give 6- and 7-acyl derivatives. 4-Acetyl-2H-1,4-benzoxazin-3(4H)-one rearranged in polyphosphoric acid exclusively to the 7-acetyl derivative. Two mechanisms are proposed to explain the different reaction sites for the acylation of 2H-1,4-benzoxazin-3(4H)-one.
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    Rate-equilibrium LFER characterization of transition states: The interpretation of α (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 1-8 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of substituents on the rate of a reaction and the effect of the same substituents on the equilibrium can often be related by a linear free energy relation (LFER): log k- = α log K= + constant, where k+ and K= are the rate constant and the equilibrium constant, respectively. This review, concentrating on group transfers, adds to many studies describing the use of α to describe the transition state. Although the use of α to describe transition states is general, group transfers constitute a simple class allowing a fairly complete description yet illustrating two often neglected contributions. Group transfers can be described by the Marcus equation relating rate to an average identity rate and the equilibrium constant; a major contributor to the slope, α, of the rate-equilibrium LFER is the variation of identity rates with substituent, rather than reflecting product-like character. Substituent effect LFERs are predominantly attributable to interaction of charges with the substituent. However, α is not an exact measure of the charge on the substituent-containing group, because in a transition state, but often not in a reaction product, there are more remote centers of charge which exert a smaller attenuated effect. A simple treatment of this attenuation for group transfers is proposed. The possibility of application of these ideas to proton transfer reactions and the interpretation of the Brønsted α (or β) is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030102
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    Maximally inhibited elimination of kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane in the gas phase. Anchimeric assistance of the phenyl group (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 77-80 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase elimination kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane were studied in a static system and seasoned vessels over the temperature range 390-450 °C and the pressure range 32-104 Torr. The reactions, under maximum inhibition of 4-fold pressure of the free-radical suppressor cyclohexene and/or propene, are homogeneous, unimolecular and obey a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for (2-bromoethyl)benzene, log k1 (s-1) = (13·04 ± 0·10) - (210·8 ± 1·3) kJ mol-1 (2·303RT)-1, and for 1-bromo-3-phenylpropane, log k1 (s-1) = (14·09 ± 0·27) - (227·7 ± 3·6) kJ mol-1 (2·303RT)-1. The phenyl group of (2-bromoethyl)benzene appears to provide anchimeric assistance in the HBr elimination of this compound. However, neighbouring C6H5 participation at the 3-position in 1-bromo-3-phenylpropane for a C-4 conformation is apparently absent. The mechanisms of these reactions are discussed.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030203
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    Hydration of 2,2-dichloro-1-arylethanones in water and tetrahydrofuran-water mixtures (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 89-94 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydration of 2,2-dichloro-1-arylethanones was studied in water and tetrahydrofuran (THF)-water mixtures and the equilibrium constants in water were estimated for four ethanones. The process is subject to specific acid and to general base catalysis. The proton inventory technique was applied to the study of the reaction in L2O and THF-L2O solutions (L = H or D). In pure water and water-rich mixtures, a very large number of protons participate in the open transition state, this number decreasing gradually with increasing water content in the mixture, until the minimum value of 2 is reached, corresponding to a cyclic, closed transition-state structure.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030205
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    Additivity of bond separation energies of hydrocarbons and their thermochemical data (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 126-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The additivity of experimental bond separation energies is demonstrated. This thermodynamic function can be reproduced by summation of group equivalents with a correction for the ‘stabilization’ energy. For this purpose, several group equivalents have been developed for alkanes and alkenes. The correlation between the computed and the experimental bond separation energies is good. These equivalents are then used in evaluating the stabilization (destabilization) energies for aromatic hydrocarbons and polyenes. The results obtained are in good agreement with values reported in the literature.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030209
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    Kinetic and spectroscopy of 2-naphthylphenylcarbene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 135-138 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Naphthylphenylcarbene (2-NPC) was studied by low-temperature EPR spectroscopy and by solution-phase laser flash photolysis. 2-NPC was found to have a triplet ground state with two distinct rotomeric forms. The triplet carbene was found to react with methanol, 1,1-diphenylethylene, styrene, carbon tetrachloride, isoprene, toluene and 2-methyltetrhydrofuran.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030210
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  • 90
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    Stereochemical studies. XXXIVPart XXXIII, I. G. Mursakulov, V. A. Svyatkin, V. V. Samoshin, N. S. Zefirov, Zh. Org. Khim. 22, 773-776 (1986).. Quantitative description of ring puckering via torsional angles. The case of six-membered rings (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 147-158 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The quantitative description of ring puckering suggested by the authors is compared with that of Cremer and Pople. The applicability of both methods is discussed for the case of six-membered rings with the use of model calculations simulating various ring distortions and with the analysis and comparison of puckering parameters computed on the basis of x-ray data for 40 six-membered rings in different cyclic structures. The 2N times reduction of the field of variation of puckering parameters for the N-membered ring is suggested and the algorithm for the renumbering of the ring atoms for this purpose is described for six-membered rings.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030304
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    Deuterium fractionation factors for carbon-hydrogen bonds: Calculations using scaled quantum-mechanical force constants (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 181-189 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The determination of uniform scaling factors for force constants calculated at the STO-3G and 4-31G levels of ab initio SCF MO theory is described; scaled 4-31G force constants provide reasonable estimates of reduced partition function ratios for deuteriated/protiated molecules. Gas-phase deuterium fractionation factors relative to methane calculated using scaled 4-31G force constants are, however, consistently too high, whereas those obtained by the MP2/6-31G* and scaled STO-3G methods are inconsistent. Scaled 4-31G deuterium fractionation factors relative to water for a range of structural moieties correlate linearly with experimental aqueous-phase values, but are also consistently overestimated. Substitution at a hydrogen-bearing carbon atom affects the deuterium fractionation factor through the combined effect of changes in reduced mass and changes in force constants other than for CH stretching.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030307
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    The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in solution (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 195-199 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in 1,2-dichloroethane solution has been studied by means of 1H NMR and UV spectroscopy and conductimetry. The influence of the nature of the anion (SbCl6-, SbCl5Br-, AsF6-) and of the methyl substituents on the rate constants of decay is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030309
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030401
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    Photochemical electrocyclization of the allyl radical into the cyclopropyl radical (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 219-229 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Following the observation that allyl radicals trapped in an argon matrix can be photolytically converted into cyclopropyl radicals (λ = 410 nm, 18 K), the IR spectrum of the cyclopropyl radical was recorded for the first time and interpreted. Bicyclopropane and cyclopropane are formed when the photolysed argon matrix is warmed from 18 to 35 K. The identification of these new species unequivocally proves the presence of cyclopropyl radicals in the photolysed matrix. This radical is shown to be a σ-type (Cs symmetry) and not a π-type (C2v symmetry) radical; of the 18 normal frequencies of the Cs cyclopropyl radical, all active in the IR, 16 were observed and were assigned to their corresponding normal modes. For this assignment advantage was taken of ab initio frequency computations reported in the literature and performed by the authors.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030403
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    Organophosphorus herbicides and plant growth regulators part 1. Synthesis and protonation behaviour of glyphosate and related compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 248-254 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ionization constants of N-phosphonomethylglycine (glyphosate) and three structurally related plant-growth regulators were determined by potentiometric titration. The effect of pD on the chemical shifts of the 1H and 13C nuclei of the methylene groups and of the 31P nucleus in these substrates was measured by NMR spectroscopy. The results allowed an assignment to be made of a specific site (carboxylic, phosphonic, ammonium) in the molecule to each of the determined pKa values.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030407
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    Concentration-dependent deuterium isotope effects on the quantum yield of arene-alkene meta photocycloaddition: The role of excimers (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 273-278 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A deuterium isotope effect on the arene-alkene meta photocycloaddition, reported earlier for toluene/toluene-d8 photoaddition to cyclopentene, was found to depend on the concentration of both arene and alkene. This phenomenon is explained in terms of an unbalanced dissociation of ‘mixed’ excimers, which play a role in the intermolecular competition experiments.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030411
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    Mechanism of α-substitution reactions of acrylic derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 285-288 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactions between acrylic esters, nitriles and similar compounds on the one hand and aldehydes and ketones on the other, catalysed by tertiary amines, lead to α-(hydroxyalkyl)acrylic compounds. Evidence on the basis of kinetics, volumes of activation and of reaction, and kinetic isotope effects is presented to deduce a mechanism in which amine first undergoes Michael addition, the resulting enolate ion adds to the carbonyl compound in a rate-determining step and finally base is eliminated. An analysis of the solvent effect on rates is also presented.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030503
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    [4]Paracyclophane: MNDO and STO-3G molecular structure and strain energyTaken in part from Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 295-300 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular structure of [4]paracyclophane was optimized at the semiempirical MNDO and the ab initio STO-3G level. A comparison of the results showed that the benzene ring is much less bent at the STO-3G level. Although some bond alternation is predicted at both levels of theory, the aromatic carbon-carbon bond lengths are still in the range typical of highly delocalized compounds. The calculated strain energy [SE(tot.)] of [4]paracyclophane is larger for the STO-3G structure. Nevertheless, the distributions of SE(tot.) over the bent benzene ring [SE(bb.)] and the oligomethylene bridge [SE(br.)] are the same for the MNDO and STO-3G structures.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030505
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    Configurations and dipole moments of O-substituted hydroximoyl cyanides. Stereoelectronic effects in the ground state of oximino compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 316-324 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dipole moments of the Z and E isomers of O-methylbenzohydroximoyl cyanides [ArC(CN)=NOCH3, Ar = C6H5 and 4-NO2C6H4], the Z isomers of benzohydroximoyl cyanides [ArC(CN)=NOH, AR = C6H5 and 4-NO2C6H4] and the Z isomers of O-benzoylbenzohydroximoyl cyanides [ArC(CN) = NOCOC6H5, Ar = C6H5 and 4-NO2C6H4] were measured. An analysis of these dipole moments indicates that anti delocalization from the OCH3 (OH) group has a small but significant effect on the overall direction and magnitude of the dipole moment. Semi-empirical molecular orbital calculations at the MNDO level support this proposal. The x-ray crystal structure of (Z)-O-methyl-p-nitrobenzohydroximoyl cyanide was carried out to confirm the configuration of the compound.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030508
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030601
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