LAUSR

Abstract The possible relationships between the HOMO energies and chemical properties (acid dissociation constants) is explored for the dihydroxybenzaldehydes (DHBs) and dihydroxy benzoic acids (DHBAs). The pK values are obtained by UV–visible spectroscopy, except for 2,6DHBA for which the pK was determined by electrochemical measurements. Cyclic voltammograms of the different compounds showed the occurrence of reversible or quasi-reversible processes, for half of the derivatives, and irreversible oxidations for the rest. From the pH dependence of the peak potentials of the oxidation peaks, the differences of the peak potentials of the dissociated and undissociated species were obtained in the same conditions of pH, buffer solution and ionic strength. These differences, showed good correlations with the values of pK, being the correlation for the aldehydes more reliable than that observed for the acids. It was concluded that the oxidation peak potentials in solution can be related to the HOMO energies. A relation between structure and chemical reactivity is proved for these derivatives.