Electron spin resonance studies. Part XV. Iminoxy-radicals from acetophenone oxime and related oximes

Abstract

The electron spin resonance spectra of the iminoxy-radicals derived by the oxidation of acetophenone oxime, some of its derivatives, and related oximes have been measured in solution. The spectra of some of these radicals have also been examined in the solid state, in which they have been generated by γ-irradiation of powdered oximes. In some cases, both syn- and anti-radicals are observed, and in other cases only one isomer; each spectrum has been assigned to a radical of a particular configuration. The results for the 2-halogenoacetophenone iminoxy-radicals in which the methyl group is trans to the iminoxy-oxygen atom show that, of the two possible conformations in which the aromatic ring and the iminoxy-function are coplanar, the one in which the halogen atom is close to the iminoxy-oxygen atom is the more heavily populated. This is in marked contrast to the situation in the radicals of the same configuration from 2-halogenobenzaldoximes, and the reason for the difference is discussed. The halogen-splittings in the 2-halogenoacetophenone iminoxy-radicals are strongly dependent on both the nature of the solvent and the temperature, unlike those in 1-halogenofluorenone iminoxy-radicals, and it is argued that, in the former series of radicals, non-planar conformations are significantly populated, though to a decreasing extent as the polarity of the solvent is increased or the temperature is lowered.