FREE-ENERGIES OF ELECTRON-TRANSFER FROM KETYLS TO ISOTOPICALLY SUBSTITUTED KETONES

A series of electron transfer competition reactions between several isotopically different benzophenones was established in liquid ammonia. The resulting electron transfer (A.- + B = A + B.-) equilibrium constants were determined via EPR studies and via the physical separation of the anion radical phase from the neutral molecule phase. This anion radical-neutral molecule separation leads to a partial separation of the isotopic isomers involved due to the deviation of the equilibrium constants from unity. Mass spectral analysis of the two phases yields thermodynamic data for the electron transfer that is consistent with the EPR results: when A = benzophenone, K(eq) at -75-degrees-C equals 0.52, 0.50, and 0.83 for equilibria involving B = perdeuteriated benzophenone, [carbonyl-C-13]benzophenone, and [sym-dodeca-C-13]benzophenone, respectively.