Substituent effects on the reaction of 2-(substituted phenyl)-4,5-dihydro-4,4,5,5-tetramethylimidazol-1-oxyl 3-oxides with nitric oxide: an experimental and MNDO study

Abstract

The relative rate constants of the oxygen transfer reaction of 2-(substituted phenyl)-4,5-dihydro-4,4,5,5-tetramethylimidazol-1-oxyl 3-oxides with nitric oxide have been measured by using liquid chromatography (h.p.l.c.). The Hammett ρ value (–0.37) indicates that electron-donating substituents favour the reaction. This can be explained by a mechanism which includes electron transfer to nitric oxide and can be rationalised by frontier orbital energies and electron densities on the nitroxyl oxygen calculated by semiempirical MNDO methods.