A thermodynamical cycle is proposed to calculate absolute pK a values for a Brönsted 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 (ΔG Mm) to the solvation energy (ΔG solv).

A thermodynamical cycle is proposed to calculate absolute pK a values for Brönsted acids in aqueous solution. The polarizable continuum model (PCM) was used to describe the solvent, and absolute pK a values were computed for different classes of organic compounds:  aliphatic alcohols, thiols, and halogenated derivatives of carboxylic aliphatic acids. The model furnishes pK a 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 Δ G solv resulting from the model adopted, the level of calculation employed, and the pK a deviations relative to the experimental results.

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