Energetics of reactions of O-sub(aq) and of O--transfer reactions between radicals

Free energies of formation of various free radicals such as O-sub(aq), CO-sub(3aq), CO-sub(2aq), and X-sub(2aq) (X = Cl, Br and I) have been derived and used to calculate standard potentials of radicals and free energies of their reactions. O-sub(aq) is an oxidizing radical with a potential E0(O-sub(aq) + H2O/2OH-sub(aq)) = 1.9 V, i.e. electron pick-up is accompanied by simultaneous breakage of a water molecule in the hydration shell. Water is also decomposed in the reaction between two O-sub(aq) radicals, HO2- + OH- being much more probable products than O + 2OH-. O-sub(aq) is almost as strong a hydrogen atom abstracting radical as the hydroxyl radical. CO-sub(3aq) can donate O- to various radicals. These reactions may occur directly or via a complex that hydrolyses. O--transfer occurs in competition with electron transfer from the substrate radical to CO-sub(3aq). Transfer of O- from CO-sub(2aq) or HCOsub(3aq) radicals to form carbon monoxide is strongly exoergic. The formation of CO in the radiolysis of acid solutions of formate is explained by O--transfer between the intermediate radicals. O--transfer from a radical to an electrode is also considered. (author)