The absolute rate constants for the reactions of Et3Si• radicals with a large number of carbonyl-containing compounds have been measured in solution by using laser flash photolysis for compounds having rate constants >105 M"1 s"1 and kinetic EPR spectroscopy for compounds having rate constants <105 M"1 s"1. The reactivities have a wide range, e.g., the rate constants at ca. 300 K are 2.5 X 109, 3.3 X 10s, 1.6 X 106, 2.8 X 10s, and 3.5 X 104 M"1 s"1 for duroquinone, benzil, propionic anhydride, diethyl ketone, and ethyl formate, respectively. Arrhenius parameters were determined for a few representative substrates. Thus for benzil, £a = (1.02 ± 0.09) kcal/mol and log (A/M"1 s"1) = 9.26 ± 0.07. Polar effects are very important in determining the reactivity of carbonyl-containing compounds toward Et3Si• radicals; e.g., reactivities are greatly enhanced by neighboring perfluoralkyl and acyloxy groups.

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