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  • 1985-1989  (5)
Collection
Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Quantum-chemical calculation of reactions involving concerted 1,2 migration of a CH3 group and 1,3(3,1)-H exchange in the propane molecule (1986)
    Springer
    Russian chemical bulletin 35 (1986), S. 1414-1417 
    Details
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusions 1. Quantum-chemical calculation by the MINDO/3 method revealed the possibility of the occurrence of concerted 1,2 migration of a CH3 group and the less favorable 1,3(3,1)-H exchange in the propane molecule, which proceed through transition states of the pseudocyclopropane type. 2. The discovered principles of model intramolecular rearrangements in two- and threecarbon fragments are in agreement with the known experimental principles of thermocatalytic reactions involving the skeletal isomerization of saturated hydrocarbons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00954814
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum chemical calculation for reactions of molecular β-elimination of hydrogen and 1,2(2,1)-H-exchange in the propane molecule (1988)
    Springer
    Russian chemical bulletin 37 (1988), S. 1599-1602 
    Details
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusions 1. A quantum chemical calculation by the MINDO/3 method predicts, for processes of 1,2(2,1)-H-exchange and concerted β-elimination of H2 in the propane molecule, lowering of the barrier by 4–8 kcal/mole compared with analogous reactions in ethane for simultaneous shift of the reaction center from the CH3 group. 2. From the calculations for model processes, in conversions of saturated hydrocarbons there can be competition between concerted reactions of dehydrogenation, skeletal isomerization, and formation of carbene centers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00961106
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum-chemical calculation of the β-elimination of H2 and the 1,2(2,1)-H exchange reaction in the ethame molecule (1986)
    Springer
    Russian chemical bulletin 35 (1986), S. 1023-1027 
    Details
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusions 1. A quantum-chemical calculation by the MINDO/3 method and a theoretical analysis have revealed the possibility of symmetry-allowed reactions involving the synchronous β-elimination of gauche-oriented H atoms from an ethane molecule and the reverse process of the supra, gauche addition of H2 to ethylene. 2. In the case of the model degenerate 1,2(2,1) exchange reaction of anti-oriented H atoms in an ethane molecule, the calculation predicts a somewhat higher activation energy in comparison toβ-elimination; however, the asymmetric transition state of this reaction is considerably more polar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00955372
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum chemical study of reactions of episulfonium ions. 1. Comparative MNDO study of opening of the episulfonium ion ring by neutral nucleophiles and SN2 substitution in protonated methylthiol (1989)
    Springer
    Russian chemical bulletin 38 (1989), S. 1439-1445 
    Details
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusions 1. From MNDO quantum chemical calculations, opening of the episulfonium ion ring by neutral nucleophiles X (X=NH3 and HCN) and related SN2 reactions of protonated methylthiol (PMT) with X proceed through formation of pre-reaction complexes in which X is coordinated either at the reacting C atom or (only in opening of episulfonium ion rings) at the center of the C-C bond. 2. In their electronic structure, the transition states for the reactions are reminiscent of a carbocation simultaneously reacting with the attacking and the leaving nucleophilic fragments (X ⋯ $$\mathop C\limits^ + $$ ⋯S). 3. Opening of episulfonium ion rings proceeds slightly more easily (Ea ∿ 10–12 kcal/mole) than substitution in PMT (Ea ∿ 22–25 kcal/mole). The ease of ring opening for episulfonium ions is due to the large exothermicity of the reaction and the lower internal activation barrier compared with SN2 reactions in PMT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00978435
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum chemical study of reactions of episulfonium ions. 2. Effect of substituents on the orientation of ring opening for episulfonium ions by neutral nucleophiles (1989)
    Springer
    Russian chemical bulletin 38 (1989), S. 1445-1450 
    Details
    ISSN: 1573-9171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusions 1. According to MNDO quantum chemical calculations, the reaction of the episulfonium ion with neutral nucleophiles X (X=NH3 and HCN) is facilitated in the presence of a methyl group at the C* atom under attack (opening in accordance with Markovnikov's rule) and is hindered in the presence of a methyl group on the adjacent C atom (opening contrary to Markovnikov's rule). Conversely, SN2 substitution of protonated alkylthiols by the same nucleophiles X is retarded upon introduction of a methyl group at the reacting atom C*. 2. Opening of the C-substituted episulfonium ion in both directions can go through the same pre-reaction complex in which the nucleophile is coordinated approximately at the center of the basal C-C bond. Opening contrary to Markovnikov's rule also can go through an alter-native pre-reaction complex in which the nucleophile is coordinated at the unsubstituted C atom. 3. Analysis of Ea and the enthalpy of reaction δH using the Marcus equation allows us to explain the apparent anomaly in the behavior of Ea upon substitution of episulfonium ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00978436
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