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A Comparison of Primary and Secondary Hydrogen Abstraction from Organophosphates by Hydroxyl Radical
Author(s) -
Burns Douglas S.,
Cory Marshall G.,
Taylor Decarlos E.,
Bunte Steven W.,
Runge Keith,
Vasey Joseph L.
Publication year - 2013
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20755
Subject(s) - chemistry , hydrogen atom abstraction , reaction rate constant , conformational isomerism , radical , thermodynamics , transition state , transition state theory , hydrogen atom , atmospheric temperature range , extrapolation , computational chemistry , kinetics , molecule , organic chemistry , quantum mechanics , catalysis , alkyl , mathematical analysis , physics , mathematics
To compare the effect of primary and secondary CH bonds on hydrogen‒atom abstraction by hydroxyl radical, rate constants for the reactions of OH radicals with trimethyl phosphate [TMPO, (CH 3 O) 3 P(O)] and triethyl phosphate [TEPO, (CH 3 CH 2 O) 3 P(O)] have been calculated using the semiclassical flux–flux autocorrelation function (SCFFAF) method and compared with experimental measurements over the temperature range 250–350 K. SCFFAF specifies that structures be obtained at the CCSD/6‒31++G** level of chemical theory and the height of the activation barrier be determined using an energy extrapolation, here a variant of the G2MP2 method. Dynamics are generated in the SCFFAF method from forces computed with a transfer Hamiltonian, which provides information about the curvature of the potential energy surface in the neighborhood of the transition state (TS), as well as the required internal forces. The temperature‒dependent reaction rate constants are calculated for the various possible abstraction pathways, primary hydrogen atom abstraction in the case of TMPO, and primary and secondary in the case of TEPO. Since two energetically favorable parent structures for each system are included in the model, the activation energy is calculated with respect to the conformer that connects to a given TS and the total rate constant at a given temperature is Boltzmann weighted with respect to the parent conformer. The computed temperature‒dependent rate curves are consistent with published experimental data in both magnitude and temperature dependence. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 187–201, 2013