ORGANIC BASED REDUCING AGENTS - PREDICTION OF OXIDATION POTENTIALS OF ELECTRON-RICH RADICALS FROM THE ANALYSIS OF AM1 CHARGE-DENSITY DISTRIBUTIONS

Electrochemical oxidation potentials of methoxy substituted benzyl, 1-naphthylmethyl, phenethyl, diphenylmethyl and cumyl radicals, substituted at the alpha-, 2-, 3-, or 4-position have been measured by photomodulation voltammetry. These data are compared to ionization potentials calculated using the AM1 molecular orbital method. Although a plot of the oxidation potentials versus the AM1 ionization potentials is quite scattered, an essentially linear relationship is found for a plot of the relative oxidation potential (i.e. compared to that of the unsubstituted parent radical) and the fraction of charge in the 2p(z) orbital of the parent cation. The relationship is remarkable considering the potentials span a range of ca. 1 eV (23 kcal mol(-1)) and the fractional charges span a range of ca. 0.5 of a unit charge. The utility of such a relationship as a predictive tool in the design of simple organic based reducing agents is discussed.