Ab initio calculations of absolute pKa values in aqueous solution I.: Carboxylic acids

A thermodynamical cycle is proposed to calculate absolute pK(a) values for a Bronsted acid in aqueous solution. The solvent (water) was represented by a dielectric using the polarizable continuum model (PCM), and the absolute pK(a) values of some aliphatic carboxylic acids were computed. The results indicate that the proposed methodology seems to be capable of predicting reasonably good absolute pK(a) values, although in some cases appreciable deviations are observed, which can be related to neglecting the molecular motion contributions (Delta G(Mm)) to the solvation energy (Delta G(solv)).