A DFT study of solvent effects on the kinetics and mechanism of the [3,3] hetero-Cope rearrangement of 1-butene thiobenzoate

Abstract

Quantum chemistry calculations have been applied to investigate the kinetics and mechanism of the hetero-Cope [3,3]-sigmatropic rearrangement of 1-butene thiobenzoate in the gas phase and different solvents. Of the two proposed mechanisms, concerted and biradical paths, a concerted mechanism with an activation Gibbs free energy of 27 kcal mol–1 was preferred. Based on natural bond orbital analysis, the electronic charge distribution at the transition state was affected by the solvent, through the perturbation in the electronic energy levels. The interaction energy of LpS25 → π*C1–C2 was larger in the solvent which means S25–C1 bond formation is more advanced in solution. C1 atomic charge reduction (0.26 e) and atomic charge increase for the S25 atom (0.23 e) indicated charge transfer from C1 to S25 during transition state formation.