Study of some mono-, di- and tricarboxylic acids in aqueous solution by the nuclear magnetic resonance technique

The nuclear magnetic resonance spectra of aqueous solutions of three β-hydroxy carboxylic acids and some of their derivatives were measured as a function of the pH. The chemical shifts of the methylene hydrogens, adjacent to the carboxyl group, exhibit titration curves. The chemical shift between the two methylene hydrogens behaves differently in each compound, the most common behaviour being the occurrence of a minimum in the shift at pH ⋍ pK. The value of the spin—spin coupling constant changes only very slightly with the pH. The effect of added neutral salts and the variation of the temperature were also investigated in some of the acids. Qualitative conclusions concerning inter- and intramolecular hydrogen bonds and electrostatic interactions in these molecules were derived from the results.