3889-74-5Relevant articles and documents
Homolytic dissociation of 1-substituted cyclohexa-2,5-diene-1-carboxylic acids: An EPR spectroscopic study of chain propagation
Jackson, Leon V.,Walton, John C.
, p. 1758 - 1764 (2007/10/03)
Hydrogen abstraction from 1-substituted cyclohexa-2,5-diene-1-carboxylic acids containing linear, branched and cyclic alkyl substituents, as well as allyl, propargyl (prop-2-ynyl), cyanomethyl and benzyl substituents, has been studied by EPR spectroscopy. For each carboxylic acid, EPR spectra of the corresponding cyclohexadienyl radicals were observed at lower temperatures, followed by spectra due to ejected carbon-centred radicals at higher temperatures. Rate constants, for release of the carbon-centred radicals from the cyclohexadienyl radicals, were determined from radical concentration measurements for the above range of substituents. The rate of cyclohexadienyl radical dissociation increased with branching in the 1-alkyl substituent and with electron delocalisation in the ejected carbon-centred radical; 3,5-and 2,6-dimethyl-substitution of the cyclohexadienyl ring led to reductions in the dissociation rate constants. Rate data for abstraction of bisallylic hydrogens from the cyclohexadienyl acids were also obtained for ethyl, n-propyl and isopropyl radicals. These results indicated a sharp drop in the rate of hydrogen abstraction as the degree of branching in the attacking radical increased. Small decreases in the hydrogen abstraction rate constants were observed for cyclohexadienes containing CO2R substituents.
The Free Radical Reaction between Alkanes and Carbon Tetrachloride
Hawari, J. A.,Davis, S.,Engel, P. S.,Gilbert, B. C.,Griller, D.
, p. 4721 - 4724 (2007/10/02)
Product studies and kinetic electron paramagnetic resonance methods were used to investigate the free radical reaction between alkanes and carbon tetrachloride in solution.Trichloromethyl radicals abstracted hydrogen from simple alkanes with rate constants of ca. 60 M-1 s-1 at 300 K. in good agreement with gas-phase data.However, rate constants for chlorine abstraction by alkyl radicals from carbon tetrachloride were ca.E4 M-1 s-1 and were therefore ca. 2 orders of magnitude higher in solution than in the gas phase.Possibilities for the origin of this effect are discussed.
A Kineic Study of the Reaction of tert-Butoxyl with Alkenes: Hydrogen Abstraction vs. Addition
Wong, P. C.,Griller, D.,Scaiano, J. C.
, p. 5106 - 5108 (2007/10/02)
Rate constants and Arrhenius parameters have been measured for the reactions of tert-butoxyl radicals with alkenes by using laser flash photolysis in benzene-di-tert-butyl peroxide (1:2 v/v) as solvent.With norbornene and norbornadiene, additions to the double bonds were the only modes of reaction, whereas with cyclopenene and cyclopentadiene, hydrogen abstraction was a competitive process.The measured activation energies were quite low; thus for norbornene, norbornadiene, and cyclopentene, Ea (kcal/mol) = 2.36 +/- 0.40, 1.56 +/- 0.55, and 2.35 +/- 0.22, respectively, while the corresponding A factors were log (A/(M-1 s-1)) = 7.76 +/- 0.31, 7.65 +/- 0.43, and 8.56 +/- 0.18, For comparison, hydrogen abstraction by tert-butoxyl at cyclopentane proceeds with Ea = 3.47 +/- 0.59 and log (A/(M-1 s-1)) = 8.47 +/- 0.45.
