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Ab initio kinetics predictions for the role of pre-reaction complexes in hydrogen abstraction from 2-butanone by OH radicals.

ABSTRACT: The existence of pre- and post-reaction complexes has been proposed to influence hydrogen abstraction reaction kinetics, but the significance still remains controversial. A theoretical study is presented to discuss the effects of complexes on hydrogen abstraction from 2-butanone by OH radicals based on the detailed PESs at the DLPNO-CCSD(T)/aug-cc-pVTZ//M06-2x-D3/may-cc-pVTZ level with five pre-reaction complexes at the entrance of the channels and four post-reaction complexes at the exit. The hydrogen bond interactions, steric effects, and contributions to the bonding orbital of the OH radical species and 2-butanone species in the complex structures were visualized and investigated by wavefunction analyses. Three kinds of mechanisms-the general bimolecular reaction, the reaction with the complexes considered, and the well-skipping reaction-were compared based on high-pressure-limit rate constants, predicted branching ratios, and fractional populations of reactants and products in the temperature range of 250-2000 K. The existence of complexes was proved to be crucial in the kinetics and mechanisms of the hydrogen abstraction from 2-butanone molecules by OH radicals.

SUBMITTER: Gao Y

PROVIDER: S-EPMC9088179 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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<i>Ab initio</i> kinetics predictions for the role of pre-reaction complexes in hydrogen abstraction from 2-butanone by OH radicals.

Gao Yi Y Zhao Yang Y Guan Qingbao Q Wang Fuke F

RSC advances 20200908 55

The existence of pre- and post-reaction complexes has been proposed to influence hydrogen abstraction reaction kinetics, but the significance still remains controversial. A theoretical study is presented to discuss the effects of complexes on hydrogen abstraction from 2-butanone by OH radicals based on the detailed PESs at the DLPNO-CCSD(T)/aug-cc-pVTZ//M06-2x-D3/may-cc-pVTZ level with five pre-reaction complexes at the entrance of the channels and four post-reaction complexes at the exit. The h ...[more]

PMID: 35547632

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Project description:The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer. Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropyl alcohol, were measured for 23 structurally different, positively charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for the reaction of three of the aryl radicals with isopropyl alcohol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of 15 different hydrogen-atom donors with two selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X-H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of 29 different aryl radicals and 18 different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be "tuned" by structural changes that influence either the vertical EA of the aryl radical or the vertical IE of the hydrogen atom donor.

Dataset Information

Ab initio kinetics predictions for the role of pre-reaction complexes in hydrogen abstraction from 2-butanone by OH radicals.

Publications

<i>Ab initio</i> kinetics predictions for the role of pre-reaction complexes in hydrogen abstraction from 2-butanone by OH radicals.

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