Electron spin resonance spectra and reactivity of aliphatic ketyl radical-anions at 77°K

Abstract

Sodium or potassium atoms have been deposited on a variety of aliphatic ketones at 77°K in a rotating cryostat and the products examined by electron spin resonance spectroscopy. The spectra show that for acetone, biacetyl, cyclopentanone, and cyclohexanone the corresponding ketyl radical-anions are formed and trapped at 77°K. The unpaired spin density on the carbonyl carbon atom of the ketyl radical-anions is only 70% of that in the corresponding alkyl radicals in which the oxygen is replaced by hydrogen. This reduction shows that there is an appreciable unpaired spin density at the carbonyl oxygen atom.

The spectra from ethyl methyl, diethyl, dipropyl, and di-isopropyl ketones show that the ketyl radical-anion is partially, or completely, replaced by a secondary radical which has been identified as that formed by hydrogen abstraction from the parent ketone. It is postulated that in all cases the ketyl radical-anions are formed initially, but that they react immediately in some of the ketones.