Relative diffusion coefficients of aromatic cations and aromatic compounds. Justification for directly equating voltammetric potentials to formal potentials

Abstract

Diffusion coefficient ratios for several aromatic compounds and the corresponding cation radicals as well as some cation radical–dication pairs were determined in acetonitrile and dichloromethane. The diffusion coefficients of the lower oxidation states were invariably found to be greater than that of the corresponding oxidized species. The ratios averaged ca. 1·3 in acetonitrile and ca. 1·5 in dichloromethane. The results were explained by an effective increase in molecular weight of the ions brought about by association with solvents and counter ions. It was concluded that the magnitudes of the diffusion coefficient ratios are not sufficiently great to bring about serious errors in the estimation of E⁰ values from voltammetric data.