Thermochemical and Kinetic Analysis on the Reactions of O2 with Products from OH Addition to Isobutene, 2-Hydroxy-1,1-dimethylethyl, and 2-Hydroxy-2-methylpropyl Radicals: HO2 Fo
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- 作者：Hongyan Sun ; Joseph W. Bozzelli ; Chung K. Law
- 刊名：Journal of Physical Chemistry A
- 出版年：2007
- 出版时间：June 14, 2007
- 年：2007
- 卷：111
- 期：23
- 页码：4974 - 4986
- 全文大小：374K
- 年卷期：v.111,no.23(June 14, 2007)
- ISSN：1520-5215
文摘
Unimolecular dissociation of a neopentyl radical to isobutene and methyl radical is competitive with theneopentyl association with O2(3
) in thermal oxidative systems. Furthermore, both isobutene and the OHradical are important primary products from the reactions of neopentyl with O2. Consequently, the reactionsof O2 with the 2-hydroxy-1,1-dimethylethyl and 2-hydroxy-2-methylpropyl radicals resulting from the OHaddition to isobutene are important to understanding the oxidation of neopentane and other branchedhydrocarbons. Reactions that correspond to the association of radical adducts with O2(3
) involvechemically activated peroxy intermediates, which can isomerize and react to form one of several productsbefore stabilization. The above reaction systems were analyzed with ab initio and density functional calculationsto evaluate the thermochemistry, reaction paths, and kinetics that are important in neopentyl radical oxidation.The stationary points of potential energy surfaces were analyzed based on the enthalpies calculated at theCBS-Q level. The entropies, S
298, and heat capacities, Cp(T), (0 
T/K 1500), from vibration, translation,and external rotation contributions were calculated using statistical mechanics based on the vibrationalfrequencies and structures obtained from the density functional study. The hindered internal rotor contributionsto S298 and Cp(T) were calculated by solving the Schrödinger equation with free rotor wave functions, andthe partition coefficients were treated by direct integration over energy levels of the internal rotation potentials.Enthalpies of formation (
Hf298) were determined using isodesmic reaction analysis. The Hf298 values of(CH3)2C
CH2OH, (CH3)2C(OO)CH2OH, (CH3)2C(OH)CH2, and (CH3)2C(OH)CH2OO radicals weredetermined to be -23.3, -62.2, -24.2, and -61.8 kcal mol-1, respectively. Elementary rate constants werecalculated from canonical transition state theory, and pressure-dependent rate constants for multichannel reactionsystems were calculated as functions of pressure and temperature using multifrequency quantum Rice-Ramsperger-Kassel (QRRK) analysis for k(E) and a master equation for pressure falloff. Kinetic parametersfor intermediate and product formation channels of the above reaction systems are presented as functions oftemperature and pressure.
) in thermal oxidative systems. Furthermore, both isobutene and the OHradical are important primary products from the reactions of neopentyl with O2. Consequently, the reactionsof O2 with the 2-hydroxy-1,1-dimethylethyl and 2-hydroxy-2-methylpropyl radicals resulting from the OHaddition to isobutene are important to understanding the oxidation of neopentane and other branchedhydrocarbons. Reactions that correspond to the association of radical adducts with O2(3) involvechemically activated peroxy intermediates, which can isomerize and react to form one of several productsbefore stabilization. The above reaction systems were analyzed with ab initio and density functional calculationsto evaluate the thermochemistry, reaction paths, and kinetics that are important in neopentyl radical oxidation.The stationary points of potential energy surfaces were analyzed based on the enthalpies calculated at theCBS-Q level. The entropies, S298, and heat capacities, Cp(T), (0 T/K 1500), from vibration, translation,and external rotation contributions were calculated using statistical mechanics based on the vibrationalfrequencies and structures obtained from the density functional study. The hindered internal rotor contributionsto S298 and Cp(T) were calculated by solving the Schrödinger equation with free rotor wave functions, andthe partition coefficients were treated by direct integration over energy levels of the internal rotation potentials.Enthalpies of formation (Hf298) were determined using isodesmic reaction analysis. The Hf298 values of(CH3)2CCH2OH, (CH3)2C(OO)CH2OH, (CH3)2C(OH)CH2, and (CH3)2C(OH)CH2OO radicals weredetermined to be -23.3, -62.2, -24.2, and -61.8 kcal mol-1, respectively. Elementary rate constants werecalculated from canonical transition state theory, and pressure-dependent rate constants for multichannel reactionsystems were calculated as functions of pressure and temperature using multifrequency quantum Rice-Ramsperger-Kassel (QRRK) analysis for k(E) and a master equation for pressure falloff. Kinetic parametersfor intermediate and product formation channels of the above reaction systems are presented as functions oftemperature and pressure.