Estimation of pKa values for carboxylic acids, alcohols, phenols and amines using changes in the relative Gibbs free energy

A relative Gibbs free energy change approach is established in this work to estimate pKa values using density functional theory at the level of B3LYP/6-31+G(d,p) theory along with a polarizable continuum solvent model (PCM). A total of 101 pKa values for 90 carboxylic acids, 56 pKa values for both alcohols and phenols, and 51 pKa values for amines, which span over 16 orders of magnitude of experimental pKa (from −0.26 to 16.10) data, have been estimated in the aqueous condition. The pKa values obtained from this study are in good agreement with the experimental results with the standard deviation of 0.37 pKa unit for the carboxylic acids, 0.40 pKa unit for both alcohols and phenols and 0.52 pKa unit for amines.