Vinyl, carboxyvinyl, and dicarboxyvinyl radicals were produced in irradiated aqueous solutions from acetylene and acetylenecarboxylic and acetylenedicarboxylic acid by addition of H atom to the triple bond or by reaction with e(aq)(-), followed by protonation. Vinyl and phenylvinyl radicals were produced by reductive dehalogenation of vinyl bromide and beta-bromostyrene with e(aq)(-). Ah these vinyl radicals react rapidly with oxygen to produce the corresponding vinylperoxyl radicals. Vinylperoxyl radicals exhibit optical absorptions in the UV (lambda(max) 250-290 nm) and in the visible range. The peaks in the visible range were at 440 nm for unsubstituted vinylperoxyl radical, between 480 and 520 nm for carboxylated vinylperoxyl, depending on pH and-number of carboxyl groups, and at 540 and 690 mm for (2-phenylvinyl)peroxyl. These vinylperoxyl radicals oxidize organic reductants such as 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonate ion) (ABTS), chlorpromazine; ascorbate, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox C) with rate constants between 4 x 10(5) and 2 x 10(9) L mol(-1) s(-1), depending on the radical and the reductant. Vinylperoxyl radicals are more reactive than similarly substituted alkylperoxyl; carboxyl and phenyl substituents on the. vinyl group increase the reactivity of the vinylperoxyl radical.