E.s.r studies of the acetyl and benzoyl radicals

Abstract

The acetyl and benzoyl radicals have been prepared by the reaction, RCOCl + Na → RĊO + NaCl, and trapped in a variety of matrices at 77 K using a rotating cryostat. Their e.s.r. spectra have been observed at 77 K and at temperatures up to 200 K. The principal values of the g-tensor and carbon-13 hyperfine coupling tensors of the carbonyl atom have been obtained for both radicals. The principal values of the proton and carbon-13 hyperfine coupling tensors have also been obtained for the methyl group in the acetyl radical. Analysis of the results shows that both radicals are σ-type radicals with an ∠RCO angle of about 130°. The unpaired electron is located primarily in a sp-hybrid orbital on the carbonyl carbon atom, but there is also an appreciable spin density on the adjacent atom of the substituent group R and on the oxygen atom. Comparison of the present results with those published for the formyl radical and the σ-radical, HOOCCH2ĊO, from malonic acid shows that the structures of the free radical centres are very similar for all four acylradicals. The spin distribution in each radical is approximately[graphic ommitted].