Electron Spin Resonance of the Acetophenone and Benzaldehyde Anion Radicals

The electron spin resonance spectra of radicals obtained from acetophenone, benzaldehyde, and 4‐fluoroacetophenone were found in a previous investigation to be inconsistent with those of other carbonyl‐anion radicals. These compounds have been reinvestigated using new techniques for the electrolytic generation of the radicals. For the first two substances, unstable radicals were detected with spectra that were different from those previously obtained. The new spectra are completely consistent with the results for the other related radicals, and also show that the carbonyl groups are locked into the plane of the aromatic ring. The nature of the radicals investigated previously has not been ascertained. A new spectrum was not obtained for the 4‐fluoroacetophenone radical under the new conditions employed for the other two radicals presumably because this species is too unstable. A preliminary interpretation has been given to linewidth variations found in the spectra.