Electronic and conformational influences on the spin density distribution in substituted tert-butyl phenyl nitroxides

Abstract

DFT calculation of the spin density distribution in tert-butyl phenyl nitroxides and phenyl nitronyl nitroxides reveals striking differences between these closely related classes of radicals. The spin density on the phenyl ring in nitronyl nitroxide radicals is due to spin polarization and only very small compared to the spin density on the ONCNO unit. In tert-butyl phenyl nitroxides, direct delocalization of the unpaired electron onto the phenyl ring leads to an almost equal distribution on the NO and phenyl groups at a coplanar geometry, which is, however, totally shifted onto the NO group when increasing the dihedral angle between the two groups.