A theoretical comparison of SN1 and SN2 reactions of saturated alkyl chlorides
Abstract
The mechanistic difference between bimolecular (SN2) and unimolecular (SN1) nucleophilic substitutions of saturated alkyl chlorides is investigated with ab initio molecular orbital (MO) calculations. The t-butyl substrate undergoes early (almost spontaneous) C–Cl bond scission, which may give double OH–(reagent) co-ordination on the carbonium cation. However, the symmetrically solvated ion, which has been accepted as a stable intermediate for racemization, is found to be located at the energy maximum of the OH– exchange reaction. The origin of racemization in nucleophilic substitution is discussed on the basis of the calculated potential surface.