The proton-abstraction by O-2(.-) from weakly acidic compounds, like aliphatic ketones (with pK(a)s approximate to 21), is endothermic and consequently slow. In this work, by employing selected aromatic ketones as proton donors (with pK(a)s approximate to 19), it has been possible to accelerate the rate of the alpha-proton abstraction by O-2(.-) to the point that it is observable within the time scale of cyclic voltammetry. Digital simulations of the cyclic voltammograms of O-2 in the presence of those ketones allow determination of the rate constants of the proton abstraction. Those rate constants were found to increase as the degree of conjugation in ketones increased, consistent with a slow endothermic rate determining step. Furthermore, because ketones as proton donors are very weak acids, it was possible to avoid any subsequent acid-base type of reaction between HO2- and the ketones, and to observe a new, kinetically reversible redox wave at E-1/2 = 0.34 V versus O-2/O-2(.-) in DMSO, assigned to the HO2./HO2- redox couple. (C) 2000 Elsevier Science Ltd. All rights reserved.