Ab Initio Studies on Acid−Base Equilibria of Substituted Phenols

Abstract

By using ab initio methods at the RHF and MP2 levels, as well as the PCM model utilizing the Gaussian 6-31++G** basis set, we calculated energies and Gibbs free energies of protonation and formation of homocomplexed anions stabilized by O···H···O bridges for 10 substituted phenol systems in the gas phase and after consideration of solvation energies in solution. The calculated protonation energies, ΔEprot, and Gibbs free energies, ΔGprot, have been found to correlate well with the acid dissociation constants in acetonitrile (AN) solutions (expressed as pKaAN values). The energies, ΔEAHA-, and Gibbs free energies, ΔGAHA-, of anionic homoconjugation do not correlate well with the experimental anionic homoconjugation constant values determined in acetonitrile.