Absolute Rate Constants for the Addition of Trimethylsilyl Radicals to Various Unsuturated Compounds

Article abstract of DOI:10.1021/ja00348a055

The absolute rate constants for the reaction of Et3Si^. radicals with a large number of unsaturated compounds have been measured by laser flash photolysis techniques.The reactivities of C=C double bonds have a wide range, e.g., the rate constants at ca. 300 K are 1.1x10⁹, 2.2x10⁸, 1.0x10⁷, 3.7x10⁶, and 9.4x10⁵ M^-1 s^-1 for acrylonitrile, styrene, tetrachloroethylene, 1-hexene, and cyclohexene, respectively.The range of reactivities for addition to aromatic and heteroaromatic compounds is rather small, the rate constants at ca. 300 K varying from 4.6x10⁵ M^-1 s^-1 for benzene to 5.0x10⁶ M^-1 s^-1 for thiophene and α-methylnaphthalene.Acetylenes are slightly less reactive than structurally analogous 1-olefins.For the other types of multiple bonds examined, reactivities decreased in the order isocyanide > nitrone > nitro > isocyanate > nitrile.Arrhenius parameters were determined for a few olefins including ethylene, for which an EPR spectroscopic competition procedure was required.For styrene, log (A/(M^-1 s^-1)) = 9.35 +/- 0.23 and E_a = 1.37 +/- 0.29 kcal/mol; for ethylene, log (A/(M^-1 s^-1))= 8.40 +/- 0.60 and E_a = 1.40 +/- 0.80 kcal/mol.