Intermolecular perturbation approach to specific solvent effects

One possible specific solvent effect, namely, the π-donor ability is considered in the light of simple intermolecular second order perturbation theory. By using the Polányi–Evans–Bell principle this theory predicts that increasing -π-donor ability of solvent should decrease the reaction rate. This prediction is fully borne out by experimental data observed for the solvent effect on 4 + 2 cycloaddition of tétracyanoethylène to anthracene.