Substituent effects on the redox potentials of dihydroxybenzenes: theoretical and experimental study

The redox reactions of p -hydroquinone and pyrocatechol undergo a two-proton-two-electron process in aqueous solution. We calculated their redox potentials at the B3LYP/6-311+G(d,p) level, and verified the values by employing cyclic voltammetry experiments. Then we selected seven substituent groups (–F, –Cl, –OH, –COOH, –CN, –NH 2 , and –NO 2 groups) to systematically investigate the substituent effect , including the sort, position, and number of the substituent, on the redox potentials of p -hydroquinone and pyrocatechol. The calculated results show that –NH 2 and –OH groups can decrease the redox potentials, while –F, –Cl, –COOH, –CN, and –NO 2 groups increase the potential values of p -hydroquinone and pyrocatechol. The calculations can accurately predict the substituent effects on the redox potentials of pyrocatechol and p -hydroquinone. We would expect that the accurate calculation results for the model systems could be applied in the prediction of electrode potentials of other molecules.