- Homogeneous Rate Constants for Coupling between Electrochemically Generated Aromatic Anion Radicals and Alkyl Radicals
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Rate constants have been measured for the coupling between hexenyl radicals and 2,2-dimethylhexenyl radicals and electrogenerated anion radicals of anthracene, 9,10-diphenylanthracene, benzophenone and quinoxaline.The rate constant for all four reactions in N,N-dimethylformamide is log k2 = 9.1(5), which is in accordance previous results in 1,2-dimethoxyethane for naphthalene and benzophenone anion radicals and 1-hexenyl radicals.The data indicate that the redox potential of the aromatic anion radical has only a minor influence on the rate of coupling with alkyl radicals.The rate constants for anion radicals of 9,10-diphenylanthracene and benzophenone were somewhat lower, 6(1) x 108 M-1 s-1, which for 9,10-diphenylanthracene might be caused by steric hindrance by the two phenyl groups.The conclusion is that the coupling reaction between aromatic anion radicals and alkyl radicals has all the characteristics of a radical-radical coupling.
- Pedersen, Steen U.,Lund, Torben
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p. 397 - 402
(2007/10/02)
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- A Convenient Method for Kinetic Studies of Fast Radical Rearrangements. Rate Constants and Arrhenius Function for the Cyclopropylcarbinyl Radical Ring Opening
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An indirect method for studying the kinetics of radical rearrangements employing N-hydroxypyridine-2-thione esters as radical precursors and hydrogen atom transfer from thiophenol as the basis trapping reaction is demonstrated in a study of an archetypal fast radical reaction, the cyclopropylcarbinyl radical ring opening.Rate constants measured over the temperature range -37 to 50 deg C gave a temperature-dependent function for the ring opening of log(k/s-1)=(13.0+/-0.14)-(6.8+/-0.2)/θ and a rate constant for ring opening at 25 deg C of 1.0E8 s-1.The kinetic values from this work were combined with rate data from low-temperature ESR studies and higher temperature nitroxyl radical trapping studies to give an Arrhenius function of log(k/s-1)=13.15-7.05/θ that is recommended for calculations of rate constants for the title ring opening.
- Newcomb, Martin,Glenn, Anne G.
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p. 275 - 277
(2007/10/02)
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