AbstractFormation and reactions of the cumyloxyl radical in aqueous solutions were studied by steady‐state and pulse radiolytic techniques. Cumene hydroperoxide reacts with e−aq(k= 4.4 × 109M−1s−1) to yield the cumyloxyl radical. The spectrum recorded after the pulse indicates formation of a species absorbing at 250 nm. This product was identified as acetophenone, which is formed by the fragmentation of the cumyloxyl radical. By comparison of the pseudo‐first‐order rates of e−aqdecay at 600 nm with the rate of production of acetophenone at 245 nm at increasing concentrations of cumene hydroperoxide, it was possible to derive a rate constant of 1.0 × 107s−1for the cleavage of cumyloxyl to acetophenone and methyl radical. This value is higher than that measured previously in organic solvents (1 × 106s−1), as expected. HPLC analysis of the radiation products acetophenone and cumyl alcohol permitted determination of rate constants for hydrogen abstraction by the cumyloxyl radical, in competition with the fragmentation. The rate constants for H abstraction from i‐PrOH, EtOH, and MeOH by CmO were found to be 9.9 × 106, 3.8 × 106, and 8.5