The Electron Spin Resonance of o-Substituted Benzophenone Ketyls

The ESR spectra of the potassium ketyls of d5-phenyl 2-methylphenyl ketone (I), phenyl 2-methylphenyl ketone (II), 2-methylphenyl 4′-t-butylphenyl ketone and 2-methylphenyl 3′-chlorophenyl ketone have been measured in a tetrahydrofuran solution. II gave four broad lines, and I, a single line with a smaller total width. It is considered that the ortho-substituted phenyl group is bent out of the plane of the three central bonds because of the steric hindrance of the ortho methyl group, and that then the free electron spin is accumulated at a non-substituted phenyl group—especially at the ortho-and para-positions. The findings on the other ketyls support the above hypothesis.