The effect of hydroxylic solvents on the solvolysis of t-butyl chloride; calculation of the cavity terms

Abstract

The effects of water and alcohols on values of ΔG^‡ for the solvolysis of t-butyl chloride have been correlated with various solvent parameters. It is shown, however, that neither simple nor multiple correlations yield information about the nature of the solvolysis because in these solvents the parameters are usually collinear. Transfer free energies of the transition state, ΔG_t°(Tr), have been correlated with ΔG_t° values for α-amino-acids and the Me₄N⁺Cl^– ion-pair. For transfers to water, these correlations are improved by correction for the size or cavity effect, using scaled particle theory, the Sinanoglu–Reisse–Moura Ramos method, or the division into neutral and electrostatic contributions. Plots of the corrected ΔG_t° values, corresponding to the solute–solvent interaction terms, for the transition state against the α-amino-acids and the ion-pair show that the transition state is very polar, though not so polar as the ion-pair, and that α-amino-acids are excellent models for the solvolysis transition state.