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 themselves useful oxidants for primary and secondary alcohols. Several computational methods were investigated in order to predict the redox potential of nitroxyl 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 lead to a useful correlation with experimental redox potential as measured by cyclic voltammetry. However, when both the N-oxo ammonium ion and the nitroxyl radical were evaluated using the Cramer-Truhlar solvation model (SM2), a linear correlation was observed between the difference in heats of formation and the experimental redox values. This correlation may be used to correctly predict the redox potential of new nitroxyl radicals.