Hammett-Taft and Drago models in the prediction of acidity constant valuesof neutral and cationic acids in methanol

The Hammett and Taft one-parameter model and Drago dual-parameter model hav e been applied to a very wide series of dissociation constants in methanol of carboxylic aliphatic acids, benzoic acid derivatives, phenols, protonate d amines, anilinium and pyridinium derivatives. Both models can be successf ully used to predict pK values in methanol of any member of the neutral and cationic acid families studied. Similarities and differences in the solvat ion behavior between the studied series of compounds have been pointed out. The relationship between the solvent dependent parameters in both models ha s been established and it shows that the Hammett-Taft rho value can be expl ained by means of the electrostatic and covalent components without any oth er contribution.