Reactivity of ketyl free radicals. Part 1.—Acid dissociation of aromatic ketyls and pinacols

Abstract

Acid-base equilibria of aromatic ketyl radicals and of their dimers (pinacols) were studied by flash photolysis of ketones and by electrochemical methods. pK values of the ketyls were found: fluorenone, 9.5; xanthone, 9.8; benzophenone, 9.15; 4-chlorobenzophenone, 9.2. The pK of the corresponding pinacols are 13.7, 13.5, 12.6 and 13.6, respectively. The difference in acidity between free radicals and their dimers is due to different hybridization of the C atom bonded to the OH group. Some new data are reported on the normal red-ox potentials of the ketone-ketyl anion systems, on the absorption spectra and dimerization rate constants of the ketyls.