Electron paramagnetic resonance spectra of aliphatic ketyl radical anions in fluid solution

Abstract

Improved methods have been developed for generating aliphatic ketyl radical anions in solution for study by EPR spectroscopy. These methods involve either photolysis of a solution of potassium in the corresponding alcohol (which probably proceeds by initial electron transfer to the solvent), or abstraction of a hydrogen atom from the corresponding alcohol by photolytically generated tert-butoxyl radicals under strongly basic conditions. The EPR spectra of a number of new aldehyde and ketone radical ions are described, and compared with the spectra of their conjugate acids. The value of a(13C-α) in the acetone radical anion is found to be 52.2 G confirming that it is non-planar. The Arrhenius parameters for the inversion of the ring in the cyclohexanone radical anion are Ea= 6.6 kcal mol–1, and log (A/s–1)= 13.2.