Structure and Acidity of Organic Compounds

Elucidation of the structures of organic acids and bases with the aid of their acidity constants is greatly hindered by their low solubilities in water and by the small quantities of material normally available. Apparent acidity constants K * can be determined potentiometrically on small samples (about 0.5 mg) for many classes of compounds of medium acidity. The apparent acidity constants K determined in the solvent system methyl cellosolvel water can be correlated, in a similar manner to thermodynamic quantities, with structural parameters (e.g. Hammett's σ * and Taft's σ * values). K values can yield information on the axial or equatorial position of carboxyl groups in cyclohexanecarboxylic acids.