ELUCIDATION OF THE MULTIPLE EQUILIBRIA OF MALVIN IN AQUEOUS-SOLUTION BY ONE-DIMENSIONAL AND 2-DIMENSIONAL NMR

One- and two-dimensional NMR were used to characterize the several for ms of malvin present in aqueous solution in the pH range 0.3-4.5 and t o determine their molar fractions as a function of pH. In addition to the flavylium cation, two hemiacetal forms and both the cis and trans forms of chalcone were firmly identified. The pathways for the interco nversion of the different forms were derived and the molar absorbances of the species calculated by coupling NMR and UV/Vis data. Equilibriu m constants were determined at different temperatures, and enthalpy an d entropy changes were calculated for the interconversion processes. T he conclusions are supported by molecular orbital calculations.