4630-45-9Relevant academic research and scientific papers
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.
ON THE REMOVAL OF METALLIC MIRRORS BY FREE RADICALS.
Rice,Tweedell
, p. 995 - 997 (2007/10/02)
Large radicals can be formed by passing chlorinated organic compounds at pressures of a few mm. , through a furnace containing a pellet of sodium and heated to 350-400 degree C. It is found that the only radicals that will remove metallic mirrors (of tellurium or antimony, etc. , previously deposited beyond the furnace) are those that can decompose into methyl or ethyl radicals plus an unsaturated molecule, without undergoing any transmigration of atoms. The authors also found, especially in the case of larger monochlorinated molecules, that there was some decomposition, approximately half, even in the absence of metallic sodium.
Heats of Formation of Radicals and Molecules by a Photoacoustic Technique
Burkey, T. J.,Majewski, M.,Griller, D.
, p. 2218 - 2221 (2007/10/02)
A photoacoustic technique was used to measure heats of free radical reactions.To illustrate the method, bond dissociation energies were measured for the Sn-H bond in n-Bu3SnH, for the C3-H bond in 1,4-cyclohexadiene, and for the C2-H bond in diethyl ether.Heats of formation of t-BuOPPh3 and t-BuOP(Bu-n)2 were determined, and the method was also used to measure quantum yields for the photolysis of di-tert-butyl peroxide and diphenyl disulfide.
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 Direct Study of the Reactions of CH2 (3B1)-Radicals with Selected Hydrocarbons in the Temperature Range 296 K
Dobe, S.,Boehland, T.,Temps, F.,Wagner, H. Gg.
, p. 432 - 441 (2007/10/02)
The kinetics of the reactions of CH2 (3B1)-radicals with five selected organic compounds has been studied in an isothermal discharge flow system in the temperature range 296 .Two basic reaction mechanisms, either direct H-atom abstarction by 3CH2 or thermal excitation of 3CH2 to the low lying 1A1 state followed by consecutive reactions of 1CH2, are of importance.For acetaldehyde, isobutane, and propane direct H-atom abstraction by 3CH2 predominates.After separation of the small contribution attributed to the singlet reaction the following rate constants for the reactions of CH2 (3B1) with acetaldehyde, isobutane, and propane are obtained: .Presuming the reactions of 1CH2 with hydrocarbons are fast the thermal excitation mechanism dominates the reaction system in the cases of methane and ethane.The activation energy of EA(CH4) = 40 +/- 8 kJ/mol measured for methane is concluded to be determined by the singlet-triplet energy splitting in CH2. - Keywords: Chemical Kinetics / Elementary Reactions / Laser Magnetic Resonance / Methylene / Radicals
Kinetics of the Reactions between CH2(3B1)-Radicals and Saturated Hydrocarbons in the Temperature Range 296 K
Boehland, T.,Dobe, S.,Temps, F.,Wagner, H. Gg.
, p. 1110 - 1116 (2007/10/02)
The reaction between CH2-radicals in their ground electronic state (3B1) and n-hexane CH2() + n-C6H14 --> CH3 + C6H13 was studied in a discharge flow system with LMR detection of CH2.In the temperature regime 413 K 4 = 1E(13.22 +/- 0.20)*exp(-3380 +/- 240/T) cm3/mol s.The reaction proceeds both via direct H-atom abstraction by CH2() and via thermal excitation of CH2() to the low-lying singlet state (1A1) followed by fast consecutive reactions of CH2().The contributions due to thermal excitation and singlet reaction were evaluated for the present work as well as for a recent study of the reactions of CH2() with a series of other hydrocarbons.Corrected rate constants kT for the direct reactions of CH2() with the reactants HR = CH4 (1), C2H6 (2), C3H8 (3), n-C6H14 (4), i-C4H10 (5), and CH3CHO (6) in the temperature range 296 K 1T = 4.3E12*exp(-42 kJ mol-1/RT) cm3/mol s, k2T = 6.5E12*exp(-33.1 kJ mol-1/RT) cm3/mol s, k3T = 4.9E12*exp(-27.7 kJ mol-1/RT) cm3/mol s, k4T = 7.8E12*exp(-25.6kJ mol-1/RT) cm3/mol s, k5T = 2.5E12*exp(-22.5 kJ mol-1/RT) cm3/mol s, k6T = 1.7E12*exp(-14.7 kJ mol-1/RT) cm3/mol s.The activation energies for the reactions studied are described by an Evans Polanyi type relation.Arrhenius expressions are proposed for the rate constants of H-atom abstraction by CH2(3B1) from primary, secondary, tertiary, and aldehydic C-H bonds.The results are compared to the isoelectronic reactions of O(3P). - Keywords: Chemical Kinetics / Elementary Reactions / Radicals / Spectroscopy, Laser Magnetic Resonance
PHOTOCHEMICAL STUDIES ON THE TERTIARY BUTYL RADICAL ISOLATED IN ARGON MATRICES
Pacansky, J.,Chang, J. S.,Brown, D. W.
, p. 257 - 260 (2007/10/02)
The t-Bu radical was isolated in an argon matrix and exposed to short wavelength UV light.Two major photoproducts were observed using IR spectroscopy: the first, isobutylene, was formed by cleavage of a βCH bond; the second was the i-Bu radical which could have been formed by a photoisomerisation, or recombination of a H atom with isobutylene.
Infrared Spectra of the Isobutyl and Neopentyl Radicals. Characteristic Spectra of Primary, Secondary, and Tertiary Alkyl Radicals
Pacansky, J.,Brown. D. W.,Chang, J. S.
, p. 2562 - 2567 (2007/10/02)
Infrared spectra are presented for the isobutyl and neopentyl radicals for the first time.Significant differences are observed in the β-Ch stretching and pyramidal bending regions between primary alkyl radicals with straigth chains and those with branched chains like the isobutyl and neopentyl radicals.These are compared with spectra of other alkyl radicals to establish characteristic infrared spectra of primary, secondary, and tertiary alkyl radicals.
