Ab Initio Calculations of Absolute pK_a Values in Aqueous Solution II. Aliphatic Alcohols, Thiols, and Halogenated Carboxylic Acids

A thermodynamical cycle is proposed to calculate absolute pKa values for Bronsted acids in aqueous solution. The polarizable continuum model (PCM) was used to describe the solvent, and absolute pKa values were computed for different classes of organic compounds:  aliphatic alcohols, thiols, and halogenated derivatives of carboxylic aliphatic acids. The model furnishes pKa values in good agreement with the experimental results for some classes of compounds. For the cases where appreciable deviations are observed, we have tried to establish a correlation among the neglected components of ΔGsolv resulting from the model adopted, the level of calculation employed, and the pKa deviations relative to the experimental results.