Sign Determination of Electron-Spin Distributions in Iminoxy Radical Analogues

Nickel-induced ¹H NMR contact shifts have been determined for β, γ, δ, and ϵ protons in a variety of oximes in which the molecular geometries are partially constrained by the oximino group. It is shown that these represent appropriate models for iminoxy radicals, with electron spin induced primarily in the nitrogen lone-pair orbital. Since this method directly provides the sign of the electron-spin density, it permits inference of the signs in the iminoxy radicals. It is pointed out that spin distributions in these radical analogues parallel those similarly determined in aliphatic and aromatic amines, thus indicating spin delocalization independence of the nature (σ or π) of the intervening bonds in the molecule.