Activation parameter changes as a mechanistic tool in SN2 reactions in solution

Abstract

Recent applications of activation parameters variation approach to the elucidation of S_N2 reaction mechanisms have led to further clarifications of structures of transition states involved in the concerted reaction pathway. S_N2 reactions in solution are reviewed with special emphasis of activation parameter variation ΔX^≠ (X = H, S and G) with substituents in the nucleophile, leaving and nonleaving groups applying linear free energy relationships in order to evaluate the resultant δΔX^≠ reaction constants. The use of internal enthalpy reaction constants δΔH^≠_int as a mechanistic tool is stressed when the structure of transition state in S_N2 reaction is changed. Variations of the activation parameters in S_N2 reactions and their mechanisms were analyzed.