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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical Studies on the Identity SN2' Reactions (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13103-13108 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100035a010
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  • 2
    Electronic Resource
    Electronic Resource
    Ab Initio studies on the rotational equilibria of 2-substituted furan and thiophene carbonyl derivatives (1996)
    Springer
    Theoretical chemistry accounts 93 (1996), S. 199-210 
    Details
    ISSN: 1432-2234
    Keywords: Rotational isomer ; SCRF ; Furan ; Thiophine ; Carbonyl derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The relative stabilities of syn- and anti-isomers of 2-substituted furan and thiophene carbonyl derivatives are investigated by theab initio MO method. The energy differences between the rotamers are 1–3 kcal mol−1 but the barriers to rotation are ca. 10 kcal mol−1 so that free rotational mode is predicted to be a rather difficult process. Application of the self-consistent reaction field (SCRF) method to account for the solvent effect indicates that the isomer with a higher dipole moment (syn) is favored in solution. An electron withdrawing 2-substituent favors syn-isomers for furan carbonyls in contrast to thiophene carbonyls for which anti-isomers are favored. These trends are ascribable to a decrease in electrostatic repulsive and attractive interactions, respectively, in the syn forms of furan and thiophene carbonyls. Contribution of non-bonded repulsive interaction in the anti-isomer is important for the relative stability of the syn-isomer of furan carbonyl derivative. Solvent effects due to higher dielectric continuum are small on the absolute values of energy differences but can reverse the order of stability of the two isomers due to a greater stability acquired by an isomer (syn) with higher dipole moment in solution. The major factor determining stability, or instability, of syn-isomer is a repulsive electrostatic interaction between the two oxygen atoms for furan carbonyls and an attractive electrostatic interaction between the sulfur and oxygen atoms for thiophene carbonyls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113417
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  • 3
    Electronic Resource
    Electronic Resource
    Ab Initio studies on the rotational equilibria of 2-substituted furan and thiophene carbonyl derivatives (1996)
    Springer
    Theoretica chimica acta 93 (1996), S. 199-210 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Rotational isomer ; SCRF ; Furan ; Thiophine ; Carbonyl derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The relative stabilities of syn- and anti-isomers of 2-substituted furan and thiophene carbonyl derivatives are investigated by the ab initio MO method. The energy differences between the rotamers are 1–3 kcal mol-1 but the barriers to rotation are ca. 10 kcal mol-1 so that free rotational mode is predicted to be a rather difficult process. Application of the self-consistent reaction field (SCRF) method to account for the solvent effect indicates that the isomer with a higher dipole moment (syn) is favored in solution. An electron withdrawing 2-substituent favors syn-isomers for furan carbonyls in contrast to thiophene carbonyls for which anti-isomers are favored. These trends are ascribable to a decrease in electrostatic repulsive and attractive interactions, respectively, in the syn forms of furan and thiophene carbonyls. Contribution of non-bonded repulsive interaction in the anti-isomer is important for the relative stability of the syn-isomer of furan carbonyl derivative. Solvent effects due to higher dielectric continuum are small on the absolute values of energy differences but can reverse the order of stability of the two isomers due to a greater stability acquired by an isomer (syn) with higher dipole moment in solution. The major factor determining stability, or instability, of syn-isomer is a repulsive electrostatic interaction between the two oxygen atoms for furan carbonyls and an attractive electrostatic interaction between the sulfur and oxygen atoms for thiophene carbonyls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113417
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical studies on the gas-phase nucleophilic substitution reactions of benzyl chlorides with phenoxides and thiophenoxides (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 115-124 
    Details
    ISSN: 0894-3230
    Keywords: cross-interaction constants ; gas-phase nucleophilic substitution reactions ; PM3 MO ; benzyl chlorides ; phenoxides ; thiophenoxides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nucleophilic substitution reactions of Y-benzyl chlorides with X-phenoxide and X-thiophenoxide nucleophiles were investigated theoretically using the PM3 semi-empirical MO method. The Leffler-Grunwald rate-equilibrium and Brønsted correlations predict that the degree of bond formation in the transition state (TS) is approximately 45 and 40% on the reaction coordinate for the phenoxides and thiophenoxides, respectively. For a weaker nucleophile, a later TS is obtained with an increased bond making and breaking. The variation of the TS structure with substituents in the nucleophile is thermodynamically controlled and is well correlated by rate-equilibrium relationships. In contrast, the TS variation (a tighter TS) with substituent (for a stronger acceptor Y) in the substrate is dependent only on variations of the intrinsic barrier and so cannot be correlated by such thermodynamically based rate-equilibrium relationships. The gas phase ρX and ρY values are much greater in magnitude than those in solution. A similar gas-phase theoretical cross-interaction constant, ρXY (ca -0.60), is obtained for both phenoxides and thiophenoxides, which is in good agreement with the experimental value (-0.62) for the thiophenoxide reactions in MeOH at 20.0 °C. The oxy and sulfur anion bases lead to a similar TS structure, but a lower reactivity for the former is due to a greater endothermicity of the reaction. A relatively wide range variation of the reaction energies, ΔG°, can be ascribed to the loss of resonance stabilization of anion nucleophiles upon product formation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical studies on the acid-catalysed aromatization of benzene-cis-1,2-dihydrodiolsDetermination of Reactivity by MO Theory, Part 92. For Part 91, see Reference 1. (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 127-131 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Theoretical studies on the acid-catalysed dehydration of 15-substituted dihydrodiols were carried out using the AM1 method. In agreement with the experimental results, the rate-limiting step is dehydration of the protonated diols, R+, and the o-phenol-forming pathway (path 1) is favoured both kinetically and thermodynamically over m-phenol product formation. The transition state for path 1 (TS 1) is found to be at an early position (ca 23% progress) along the reaction coordinate and a better correlation of the rate constant is obtained with σ+. Three resonance forms can exist for the benzenonium intermediate but the contribution of one form is dominant in the later TS, which resembles the cationic intermediate. The contribution of the other two, however, weakens the σ+ effect of +M subsituents. The σP correlation of the rate constant in acid solution is therefore suggestive of a later TS resembling the cationic intermediate which is stabilized by solution.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610080213
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical studies on the transition-state imbalance in malononitrile anion-forming reactions in the gas phase and in water (1997)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 10 (1997), S. 908-916 
    Details
    ISSN: 0894-3230
    Keywords: AM1-SM2.1 ; transition-state imbalance ; benzylidenemalonotriles ; nucleophilic additions ; Brønsted coefficients ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: ---Semiempirical MO theoretical studies were carried out on the nucleophilic addition of phenoxide nucleophiles to 1,1-dicyano-2-arylethenes in the gas phase and in water using the AM1 method and the Cramer-Truhlar solvation model SM2.1. The gas-phase αn and βn values are 0·81 and 0·65, respectively, leading to the positive imbalance of I=0·16; the electric polarization and dispersion interactions of water incorporated in the SM2.1 model reduce both the αn and βn values to 0·61 and 0·36, giving I=0·25. The two Brønsted coefficients obtained theoretically in water agree satisfactorily with the experimental values (αncorr=0·55 and βn=0·35) obtained with amine bases. The small imbalance found both theoretically (I=0·25) and experimentally (I≈0·20) can be ascribed to (i) a near-zero distance factor, Δd=dp-dTS≈0 and (ii) the small extent of negative charge localization by strucutral reorganization in the transition state. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical studies on the reactions of substituted phenolate anions with formate estersDetermination of Reactivity by MO Theory. Part 91. For Part 90, see Ref. 1. (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 325-334 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semiempirical MO (PM3) studies are reported on the reactions of 18 substituted phenolate anions with m-(MNPF), p-(PNPF) and 3,4-dinitrophenyl formates (DNPF). The mechanistic change from rate-limiting formation to breakdown of the anionic intermediate (T-) can occur in the gas phase, especially for MNPF, at approximately an equal proton affinity (PA) of the nucleophile and leaving group phenolates, i.e. ΔPA = 0 as the PA of the phenolate anion is decreased. In solution, however, owing to the low stability of T and a greater stabilization by solvation of the transition state for the breakdown step (TS2), all three formate esters are predicted to proceed by a concerted mechanism, which is in agreement with the experimental results. The low stability of T can be ascribed to the relatively high electron affinity of the phenolate anions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610080502
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical studies of the identity allyl transfer reactionsDetermination of Reactivity by MO Theory, Part 85. For Part 84, see Ref. 1. (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 473-483 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio studies on the SN2 identity exchange reactions RCH2X + X- → X- + RCH2X for R = CH2CH with X- = H, NH2, OH, F, PH2, SH and Cl, and for R = CH3 and CH≡C with X- = Cl were carried out at the HF and MP2 levels using the 6-31 ++ G** basis sets. The activation barriers, ΔE≠, and major structural changes, Δd≠ (C-X), in the activation process are closely related to the electronegativity of the R and X groups. The effect of electronegativity is twofold: a stronger electronegativity of R and/or X leads to a lesser electronic as well as structural reorganization required in the activation and to a greater correlation energy in the transition state. The former effect lowers the energy barriers at both the HF and MP2 levels whereas the latter lowers only the correlated (MP2) activation energies. Results with R = CH2CH, as a model for R = C6H5, indicate that ‘benzylic effect’ arises mainly from the relatively stronger electron acceptor ability of the phenyl group.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610080706
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  • 9
    Electronic Resource
    Electronic Resource
    Ab initio molecular orbital studies of nonidentity allyl transfer reactions (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 16 (1995), S. 1045-1054 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio molecular orbital (MO) calculations are carried out on the nonidentity allyl transfer processes, X- + CH2CHCH2Y ⇌ CH2CHCH2 X + Y-, with X- = H, F, and Cl and Y = H, NH2, OH, F, PH2, SH, and Cl. The Marcus equation applies well to the allyl transfer reactions. The transition state (TS) position along the reaction coordinate and the TS structure are strongly influenced by the thermodynamic driving force, whereas the TS looseness is originated from the intrinsic barrier. The intrinsic barrier, ΔE0
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540160811
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio studies of three-membered ring formation through intramolecular nucleophilic substitution (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1773-1784 
    Details
    ISSN: 0192-8651
    Keywords: three-membered ring formation ; intramolecular nucleophilic substitution ; ab initio molecular orbital method ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Three-membered ring (3MR) forming processes of -X(SINGLE BOND)CH2(SINGLE BOND)CH2(SINGLE BOND)F and -CH2(SINGLE BOND)C((SINGLE BOND)Y)(SINGLE BOND)CH2(SINGLE BOND)F (X(DOUBLE BOND)CH2, O, or S and Y(DOUBLE BOND)0 or S) through a gas phase neighboring group mechanism (SNi) are studied theoretically using the ab initio molecular orbital method with the 6-31+G* basis set. When electron correlation effects are considered, the activation (ΔG≠) and reaction energies (ΔG0) are lowered by ca. 10 kcal mol-1, indicating the importance of the electron correlation effect in these reactions. The contribution of entropy of activation (-TΔS≠) at 298 K to ΔG≠ is very small, and the reactions are enthalpy controlled. The ΔG≠ and ΔG0 values for these ring closure processes largely depend on the stabilities of the reactants and the heteroatom acting as a nucleophilic center. The Bell-Evans-Polanyi principle applies well to all these reaction series.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1773-1784, 1997
    Additional Material: 6 Ill.
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