The reactions of alpha-hydroxyl and alpha-alkoxyl alkyl radicals with methanesulfonyl chloride (MeSO2Cl) have been studied by pulse radiolysis at room temperature. The alkyl radicals were produced by ionizing radiation of N2O-saturated aqueous solution containing methanol, ethanol, isopropanol, or tetrahydrofuran. The transient optical absorption spectrum consisted of a broad band in the region 280-380 nm with a maximum at 320 nm typical of the MeSO2 center dot radical. The rate constants in the interval of 1.7 X 10(7)-2.2 x 10(8) M-1 s(-1) were assigned to an electron transfer process that leads to MeSO2Cl center dot-, subsequently decaying into MeSO2 center dot radical and Cl-. The rate constants for the addition of CH3SO2 center dot to acrolein and propiolic acid were found to be 4.9 x 10(9) M-1 s(-1) and 5.9 x 10(7) M(-1)s(-1), respectively, in aqueous solutions and reversible. The reactivity of tosyl radical (p-CH3C6H4SO2 center dot) toward a series of alkenes bearing various functional groups was also determined by competition kinetics in benzene. The rate constants for the addition of tosyl radical to alkenes vary in A much narrower range than the rate constants for the reverse reaction. The stabilization of the adduct radical substantially contributes to the increase of the rate constant for the addition of tosyl radical to alkenes and, conversely, retards the beta-elimination of tosyl radical.