| Résumé | A variety of transient RnM· radicals (M = C, Si, Sn, and P, but not O) have been trapped with di-tert-butyl thioketone and the persistent adduct radicals, RnMSĊ(CMe3)2 (1). have been examined by EPR spectroscopy. From a comparison of the hyperfine splittings by M in 1 and in RnMCH2Ċ(CMe3)2 and analogous radicals, and from a consideration of the g values for 1 (2.0024-2.0033), it is concluded that the RnM group eclipses the Cα 2pz orbital. Competitive experiments involving the reaction of tert-butyl with thione or oxygen at -80°C and the reaction of methyl with thione or Me3CNO at -40°C indicate that alkyl addition to the thione has a rate constant of ca. 106 M-1 s-1 at these temperatures. The CH3SĊ(CMe3)2 radial exists in equilibrium with a dimer at temperatures in the range -70 to -110°C: ΔH = 9.6 ± 1.5 kcal/mol; ΔS = 32 ± 3 gibbs/mol. Above -50°C the CH3SĊ(CMe3)2 radical decays with the first-order kinetics. It is concluded that CH3SĊ(CMe3)2 and SiH3SĊ(CMe3)2 decay by an intramolecular transfer of H from M to Cα. The CF3SĊ(CMe3)2 radical is extremely persistent. The (n-Bu)3SnSĊ(CMe3)2 radical decays with second-order kinetics. Arrhenius parameters for some of the decay reactions are reported. |
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