| Résumé | Laser flash photolysis (LPF) techniques with detection in the infrared and in UV-visible regions of the spectrum have been used in combination with detailed product studies to assess solvent effects on the hydrogen abstraction and β-scission reactions of cumyloxyl radicals. The variation in the ratio of the products of these two competing processes in solvents with different polarities is due to the solvent's influence on β-scission. The rate constants for β-scission at 30°C, k β CumO, were (2.6 3 ± 0.2 4) × 10 5, and (19 .6 ± 3 .4 × 10 5s -1 in CCl4, C 6H 6, C 6H 5Cl, (CH 3) 3COH, CH 3CN, and CH 3COOH, respectively. The rate constant for hydrogen abstraction from cyclohexane were essentially identical in these six solvents, viz., k a CumO = (1.2 4 ± 0.1 2) × 10 6 M -1 s -1. There is a reasonably good linear correlation between log (k β CumO/s -1) and certain cybotactic solvent parameters indicating that solvent effect on k β CumO are due to a localized interaction between the transition state for β-scission and adjacent solvent. |
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