Prediction of transition state configuration in concerted reactions from the energy requirements of the separate processes

Abstract

A simple method is presented for calculating the configuration and energy of the transition state in a concerted reaction from the energies required to form the intermediates of the hypothetical step-wise processes. The model is tested by comparison of predicted and observed structure-reactivity relations. Substitution in the attacking or leaving portion of a concerted reaction system should give rise to changes exclusively in the more remote bond and hence to a linear free energy relationship, while non-linear correlations are possible when substitution occurs in the central moiety. Taken n conjunction with experimental evidence, the model suggests that in carbonyl hydration reactions nucleophilic attack occurs synchronously with a single proton transfer. The conditions favouring bifunctional catalysis are discussed.