Ab initio calculations on pKa values of benzo-quinuclidine series in aqueous solvent

The Conductor-like Polarizable Continuum Model (CPCM) in conjunction with the radii of UAHF, UAKS, Pauling, Bondi and KLAMT was used to calculate the pKa values of benzo-quinuclidine series in aqueous solvent. Comparison of calculated pKa’s and experimental data indicates that the accuracy of the CPCM model predominantly depends on the choice of cavity models. The most accurate pKa’s were obtained from the use of CPCM with UAKS or UAHF cavity, producing a mean absolute deviation of 0.39 and 0.40 pKa units, respectively. These methods are suitable for calculating the pKa’s of the relatively large ammonium ions in aqueous solution.