| Résumé | 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 1.1 × 109, 2.2 × 108, 1.0 × 107, 3.7 × 106, and 9.4 × 105 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 4.6 × 105 M-1 s-1 for benzene to 5.0 × 106 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 Ea = 1.37 ± 0.29 kcal/mol; for ethylene, log (A/(M-1 s-1)) = 8.40 ± 0.60 and Ea = 1.40 ± 0.80 kcal/mol. © 1983 American Chemical Society. |
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