Prediction of pKa values of phenolic and nitrogen-containing compounds by computational chemical analysis compared to those measured by liquid chromatography.

The pKa values of 64 phenolic and 50 nitrogen-containing compounds were obtained by reversed-phase liquid chromatography and computational chemical calculation. The chromatographically obtained values of phenolic compounds were equal to pKa values from references and Hammett's equation, and those of nitrogen-containing compounds were lower than the reference values. It appeared difficult to calculate the properties of the ortho effect and nitro group by the computational calculation method. However, the calculation was simpler than selecting different constants of Hammett's equation for a variety of compounds.