Absolute Rate Constants for the Addition of Triethylsilyl Radicals to the Carbonyl Group

Article abstract of DOI:10.1021/ja00383a021

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, E_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 enchanced by neighboring perfluoroalkyl and acyloxy groups.