AbstractThe kinetic and mechanistic properties of alkoxy radicals in organic solvents are briefly reviewed. Owing to the scarcity of such data in aqueous solutions and since reactions at the membrane/water interface may be also biologically important, we have studied the reactivity of these radicals in water and the results of our investigations are reported. Alkoxy radicals were generated by photolytic or radiolytic cleavage of peroxide precursors (tert‐butyl hydroperoxide and di‐tert‐butyl peroxide as well as hydroperoxides of polyunsaturated fatty acids). A quantitative correlation between the structure of various substances, in particular phenolic antioxidants, and their activity in inhibiting the alkoxy radical‐induced bleaching of the water‐soluble carotenoid crocin will be discussed. Rate constants forintermolecular reactions oft‐BuO radicals were determined by pulse radiolysis. The diffusion‐controlled reaction with the catechol antioxidant nordihydroguaiaretic acid demonstrates an effective competition with the very rapidintramolecularβ‐fragmentation in water. The results support the view that a considerable amount of alkoxy radicals interact with substrates before they can rearrange