| Résumé | Alkoxytriphenylphosphoranyl and boranyl radicals have been observed using optical absorption spectroscopy. Kinetic measurements of the formation of these species provide the first absolute measurements of radical attack at the phosphorus and boron centers. For tert-butoxy radical attack at 22°C the rate constants are 1.9 × 109 and 1 × 108 M-1 s-1 for Ph3P and Ph3B, respectively. The radicals so produced decay with lifetimes of 900 and 15 μs, respectively. Methoxytriphenylphosphoranyl radicals are produced in the radiolysis of methanolic solutions of triphenylphosphine; a reinterpretation of earlier experiments in the field is suggested. In the case of triphenylphosphine the radicals have been examined using laser flash photolysis, ESR spectroscopy, pulse radiolysis, and conventional flash photolysis, the various techniques providing mutually supporting results. In the case of triphenylborane our results provide for the first time conclusive evidence for the stepwise nature of radical reaction at the boron center. © 1979 American Chemical Society. |
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