Reactivity–selectivity relationships. Part 12. Intermediates formed in the solvolysis of substituted benzyl derivatives. The importance of HOMO–LUMO interactions in determining selectivity
Abstract
The intermediates undergoing nucleophilic attack during the solvolysis of a series of substituted benzyl derivatives in aqueous ethanol are examined in the presence of m-chloroaniline. Conclusions are based on the measurement of substrate selectivity towards the competing nucleophiles, ethanol and m-chloroaniline and the application of perturbation molecular orbital (PMO) theory. The results suggest that p-chlorobenzyl, benzyl, and p-methyl benzyl chlorides undergo nucleophilic attack on intimate ion pairs while p-methoxybenzyl chloride undergoes attack on solvent separated ion pairs. These conclusions are in accord with a previous study on benzyl derivatives utilizing ethanol and water as competing nucleophiles. The importance of HOMO–LUMO interactions in determining substrate selectivity in nucleophilic substitution reactions, using two dissimilar nucleophiles, is confirmed.