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 × 109, 3.3 × 108, 1.6 × 106. 2.8 × 105, and 3.5 × 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, Ea - (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. © 1982 American Chemical Society.