The ab initio E • might agree quantitatively with the experimental value; however the two are not directly equivalent due to cell resistance, concentration dependence or a lack of better solvation treatment in calculations. Therefore, the potentials were calculated relative to those of a reference compound, rather than as absolute potentials, in order to remove the influence of systematic errors between the experimental conditions used here and those used to determine absolute potentials of reference compounds reported elsewhere. AQ was chosen as the reference compound and isodesmic reaction schemes for the reduction and oxidation of are given as follows: