Cross conjugated free radicals. 1. An ESR and CNDO/INDO study of the geometry and electronic structure of substituted benzoylmethyl radicals

The ESR spectra of a series of benzoylmethyl radicals are reported which exhibit resolved hyperfine splittings from nuclei of the substituted phenyl ring. INDO/CNDO calculations show that the preferred conformation of such radicals have a twisting angle of about 45° between the plane of the phenyl ring and the plane of the carbonylmethyl fragment. Strongly electron-donating or -withdrawing para substituents are believed to render a planar conformation more likely via the admixture of p-quinoid resonance structures. © 1979 American Chemical Society.