Reactivity of aryl and vinyl radicals: abstraction of hydrogen atom or reaction with a nucleophile

The reactivities of aryl and vinyl radicals, two fundamental transient intermediates, have been investigated with respect to two elementary processes: H-atom abstraction and reaction with a nucleophile (Y-, in the S(RN)1 reaction). The radicals of interest were generated from haloarene or haloethene precursors, either by use of the BU3SnH/AIBN system or by photostimulated electron transfer from a nucleophile, and the partition of the intermediate radical between competing pathways was investigated. Use both of indirect methods (such as the study of the reaction products in competition experiments; use of a radical-clock probe) and of direct ones (such as the detection of the radicals by flash photolysis experiments) enabled the following rate constants to be obtained (all values in m(-1.)s(-1) at 25 degreesC). For phenyl-type radicals, the rate constants for H abstraction (k(H)) from the solvents Me2SO (2.8(.)10(6)) and CH3CN (6.7(.)10(6)) and the rate constant for combination with ...