A quantum mechanical study of proton exchange in sulfoxides with retention and inversion of configuration

A survey of the experimental data on the structures of α-sulfonyl and α-sulfinyl carbanions is presented as an introduction to the present work, a theoretical study of hydrogen methyl sulfoxide (HMSO) and hydrogen methylsulfinyl anion (HMSO−) by nonempirical self consistent field (s.c.f.) calculations using Gaussian basis sets. Calculations on dimethyl sulfoxide (DMSO) and its conjugate base (DMSO−) are also presented and fully justify the choice of HMSO and HMSO− for the detailed work. A conformational energy surface (total energy as a function of rotation about the C—S bond and inversion of the carbanion angle) for HMSO− is presented and used to determine the stereochemical fate of a carbanion generated next to a sulfinyl group. Predictions are made concerning the probable course of proton exchange next to S—O and an explanation is offered for the experimental facts concerning exchange in sulfoxides. A very significant finding is that postulation of d-orbital conjugation is not essential to explain the asymmetry of α-sulfinyl carbanions.