AM1-SM2 calculations model the redox potential of nitroxyl radicals such as TEMPO

Nitroxyl radicals can be oxidized to N-oxo ammonium salts that are themselv es useful oxidants for primary and secondary alcohols. Several computationa l methods were investigated in order to predict the redox potential of nitr oxyl radicals and to better understand the behavior of different nitroxides as catalysts for alcohol oxidation. The difference in calculated heats of formation for N-oxo ammonium ions and nitroxyl radicals using AM1 did not l ead to a useful correlation with experimental redox potential as measured b y cyclic voltammetry. However, when both the N-oxo ammonium ion and the nit roxyl radical were evaluated using the Cramer-Truhlar solvation model (SM2) , a linear correlation was observed between the difference in heats of form ation and the experimental redox values. This correlation may be used to co rrectly predict the redox potential of new nitroxyl radicals.