Absolute rate constants and Arrhenius parameters for hydrogen abstractions (from carbon) by the t-butoxyl radical ((t) BuO.) are reported for several hydrocarbons and tertiary amines in solution. Combined with data already in the literature, an analysis of all the available data reveals that most hydrogen abstractions (from carbon) by (t) BuO. are entropy controlled (i.e., TdeltaS > deltaH, in solution at room temperature). For substrates with C-H bond dissociation energies (BDEs) > 92 kcal/mol, the activation energy for hydrogen abstraction decreases with decreasing BDE in accord with the Evans-Polanyi equation, with alpha approximately 0.3. For substrates with C-H BDEs in the range from 79 to 92 kcal/mol, the activation energy does not vary significantly with C-H BDE. The implications of these results in the context of the use of (t) BuO. as a chemical model for reactive oxygen-centered radicals is discussed.

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to four of the reactors in the amounts of 0.058,0.114, 0.231, and 0.478 mmol. The closed reactors were immersed in a thermostatic oil bath held at 170 °C for 20 h. Products were washed from the reactors with terf-butylbenzene. Capillary gas chromatographic analysis of the products confirmed that the ratios of tetralin to tetralin-d12 remained essentially unchanged over the course of the reaction. In this analysis, tetralin was cleanly separated from tetralin-d12. Toluene was isolated from the reaction mixture using preparative packed-column gas chromatography and collected in glass-wool-packed U-tubes immersed in a dry ice/acetone bath. The ratio of toluene to toluene-dj was determined by measuring the relative intensities at masses 92.0626 and 93.0689 with a Kratos MS-50 high-resolution mass spectrometer at an ionizing voltage

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The chlorine atom cage effect was used as a highly sensitive probe for studying the effect of viscosity and the possible role of solvent clusters on cage lifetimes and reactivity for reactions carried out in supercritical fluid solvents. These experiments were conducted in supercritical carbon dioxide (SC-CO2, 40 °C, at various pressures) with parallel experiments in conventional solvents and in the gas phase. The results of these experiments provide no indication of an enhanced cage effect near the critical point in SC-CO2 solvent. The magnitude of the cage effect observed in SC-CO2 at all pressures examined is well within what is anticipated on the basis of extrapolations from conventional solvents.