THEORETICAL-STUDIES OF THE IDENTITY ALLYL TRANSFER-REACTIONS

Ab initio studies on the S(N)2 identity exchange reactions RCH(2)X + X (-) --> X(-) + RCH(2)X for R = CH2CH with X(-) = H, NH2, OH, P, PH2, S H and Cl, and For R = CH3 and CH = C with X(-) = Cl were carried out a t the HF and MP2 levels using the 6-31++G* basis sets. The activation barriers, Delta E+, and major structural changes, Delta d(not equal)( C-X), in the activation process are closely related to the electronega tivity of the R and X groups, The effect of electronegativity is twofo ld: a stronger electronegativity of R and/or X leads to a lesser elect ronic as well as structural reorganization required in the activation and to a greater correlation energy in the transition state, The forme r effect lowers the energy barriers at both the HF and MP2 levels wher eas the latter lowers only the correlated (MP2) activation energies, R esults with R = CH2CH, as a model for R = C6H5, indicate that 'benzyli c effect' arises mainly from the relatively stronger electron acceptor ability of the phenyl group.