ALIPHATIC KETONE ANION-RADICALS - A MATRIX-ISOLATION ESR STUDY

Aliphatic ketone anions (ketyl radicals) were produced by cocondensing aliphatic ketones and Na atoms in argon matrices at similar to 4 K an d effecting electron transfer between them by mild radiation (lambda = 590 nm). ESR spectra of anion radicals of acetone, diethyl ketone, di isopropyl ketone, tert-butyl methyl ketone, and cyclobutanone were thu s observed and analyzed. Examination of the acetone anion by ab initio SCF (UHF) and semiemperical (AM1) molecular orbital calculations yiel ded the structure and the conformation (of the methyl groups) in reaso nable agreement with those deduced from the observed beta proton and a lpha C-13 hyperfine coupling tensors. It is concluded that these anion s have a semioccupied molecular orbital (SOMO) of the form R(2)C-O- (7 0%) <----> R(2)C(-)-O (30%) and are pyramidal in shape at the a carbon . In argon matrices at similar to 4 K, the beta alkyl groups are locke d at a given azimuthal position, and the beta proton situated about th e position trans to the unpaired electron orbital at the a carbon has a singularly large hyperfine coupling constant.