Comprehensive Studies on the pKa of Substituted Benzoic Acids: A Theoretical Study

초록

To investigate the origin of substituent effects on the acidity of benzoic acids, a series of substituted benzoic acids have been examined theoretically at various levels of theory. A more satisfactory agreement with the experimental values was obtained at the G3(+)MP2 level on the MP2/6-31+G* geometries. To make accurate predictions of pKa values in aqueous solution, the structures and the Gibbs free energies of solvation were examined by use of the conductor-like polarizable continuum model (CPCM) with various cavity models: UA0, UAHF, UAKS, UFF, BONDI and PAULING, and by use of a discrete/continuum solvation model at the MP2/6-31+G* levels. Geometries of the stationary point species in aqueous solution and gas-phase have also been fully optimized and characterized by frequency calculations. All the calculations were performed with the Gaussian-03 program.