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  • 1
    Electronic Resource
    Electronic Resource
    Theoretical studies on nitrile-forming elimination reactionsDetermination of Reactivity by MO Theory, Part 73. Part 72, 1. Lee, C. K. Kim, B. H. Kong and B. C. Lee, J. Phys. Org. Chem. 4, 449 (1991). (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 259-268 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The base-promoted nitrile-forming elimination reactions of YCH=CHCβH=NOCH=CHZ (Y=OCH3, H or Cl and Z=H or NO2) were studied by the AM1 MO theoretical method with Cl- as a base. The reaction is found to proceed by an E1cB-like E2 mechanism in which Cβ - H bond cleavage is more advanced than N - O bond breaking. The syn-elimination has a more E1cB-like transition state (TS) than the anti elimination, which is attributed to the structurally favourable nN - ó * (Cβ - H) charge-transfer interaction. An electron-withdrawing Y substituent lowers the activation barrier by stabilizing negative charge developed on Cβ in the TS. An electron-withdrawing substituent in the leaving group (Z = NO2) tends to enhance the anti relative to the syn elimination process by depressing the δ*(N - O) level, which in turn makes the nć - δ*(N - O) interaction more effective. The YCH=CH -  and  - CβH=N fragments are perpendicular in the TS, which is stabilized by delocalization of negative charge developed on the Cβ atom.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050507
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  • 2
    Electronic Resource
    Electronic Resource
    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 
    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 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.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030502
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  • 3
    Electronic Resource
    Electronic Resource
    AM1 studies on the acid hydrolysis of acetamide (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 397-403 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The A2 hydrolysis of acetamide was investigated using the AM1 method and the results were compared with those of MNDO. The two methods agree in the general mechanism but differ in detail; MNDO assigns an unduly high energy for a complex with long bonds in contrast to AM1 and ab initio (at the 3-21G and 6-31G levels) methods, which predict a stable structure for such a complex. Inclusion of solvate water molecules has the effect of lowering activation barriers in general. An increase in the number of solving molecules up to four results in narrowing of the activation energy gap between the two rate determining steps of the A2 hydrolysis of the N- and O-protonated acetamide, but no reversal of the relative order of the barrier occurs; the A2 hydrolysis proceeding through the less stable N-protonated tautometer is therefore likely to remain as a major reaction path in solution-phase reactions, in agreement with experimental results.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030608
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical studies on the gas-phase rearrangement of deprotonated allyl phenyl etherDetermination of Reactivity by MO Theory, Part 80. For Part 79, see Ref. 1. (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 812-818 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Wittig and anoinic Claisen rearrangements of deprotonated allyl phenyl ether, PhOC̄HCH=CH2, were investigated by MO theory employing the AM1 method. The most favoured reaction pathway for the Wittig rearrangement is the intramolecular SNAr process proceeding by the addition-elimination mechanism involving a Meisenheimer complex-type, three-membered-ring intermediate. For the anionic Claisen rearrangement a three-step mechanism is favoured, in which the intramolecular proton transfer occurs first from the ortho position of the phenyl ring to the anionic carbon centre, which is then followed by a process involving a six-membered ring intermediate. The two types of rearrangements can compete, but the Wittig type is more facile and favoured than the Claisen process owing to the lower activation enthalpy. The results are in good agreement with gas-phase experimental results.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610051206
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical studies of substituent effects on thermal eliminations of aryl ethyl carbonates and S-aryl O-ethyl thiocarbonatesDetermination of Reactivity by MO Theory. Part 82. (1993)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 215-222 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Substituent effects on the thermal elimination reactions of carbonates and thiocarbonates were investigated MO theoretically using the AM1 method. For both substrates, an electron-withdrawing group is found to facilitate the decomposition. A two-step process is favoured by carbonates, whereas one- and two-step processes can compete in the pyrolysis of thiocarbonates. The ability to transmit substituent effect is greater with oxygen (carbonates) than with sulphur (thicarbonates) in contrast to the experimental results of Taylor and co-workers. Modelling studies with replacement of the phenyl ring with a vinyl group are found to be justified in this type of work.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610060404
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  • 6
    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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  • 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
    Theoretical studies on the gas-phase smiles rearrangementDetermination of Reactivity by MO Theory, Part 71. For Part 70, see Ref. 1. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 315-329 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase Smiles rearrangements and SNi processes of ions C6H5X(CH2)nY- (X, Y = 0 or S, and n = 2-4) have been studied by the AM1 MO method. The Smiles rearrangement to an ortho position of the phenyl ring is diffcult owing to involvement of a high-energy barrier process involving a 1,2-hydrogen shift. The reactivity of the Smiles rearrangement to the ipso position increases in the order X — O and Y — S 〈 X — S and Y — O 〈 X — Y — 0 as a result of steric and electronic effects in the transition state (TS). The reactivity order with respect to the side-chain length, n = 3 〈 4 〈 2, is mainly determined by ring strain in the TS. For the SNi process, in which Y attacks the β-carbon (β to phenyl), the enthalpy (δH≠) factor becomes more favourable but the entropy (δS≠) factor becomes unfavourable with an increase in the side-chain length, in agreement with a general trend for cyclization processes. The product ratio in the Smiles rearrangement and the SNi process is largely controlled by the thermodynamic stabilities of the products, as observed in gas-phase experiments.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040509
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