Use of steric effects in determining the position of the transition state for the SN2 reaction between methyl iodide and Δ4-thiazoline-2-thiones

Abstract

The quantitative nucleophilic reactivity of some 3-alkyl-Δ⁴-thiazoline-2-thiones (1) towards methyl iodide is described. Bulky alkyl groups increase the rate of S-alkylation and this unexpected behaviour is explained by strain release in the transition state. It is shown that the rate acceleration is closely related to the conformational state of the 3-alkyl group. Using steric effects to examine the transition state, we have shown that it is, in regard to the heterocyclic ring, 65% along the reaction co-ordinate from the initial state.