PREDICTIONS OF ISOTOPE EFFECTS IN SN2 REACTIONS

A simple semiempirical model is suggested for the description of the energy barrier in SN2 transition states. The model is based on an adaption of the Johnston equation.It supplies a basis for the evaluation of the force constants F11,F22,and F12 of the transition state, whose values must be known for complete predictions of kinetic isotope effects. The constants of the model for a particular reaction may be derived from experimental δG ≠ and δG values.— The influence of the nucleophilicpowers of entering and leaving groups on the constants of the energy barrier is discussed in some detail. It is suggested to carry out a new evaluation of the problem of nucleophilic reactivity on a wider basis, with consideration of rate data, as well as of equilibrium data. © 1969, Walter de Gruyter. All rights reserved.