Ab initio calculations of absolute pK(a) 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 r easonably good absolute pK(a) values, although in some cases appreciable de viations are observed, which can be related to neglecting the molecular mot ion contributions (Delta G(Mm)) to the solvation energy (Delta G(solv)).