Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Braña, Pedro; Sordo, José

doi:10.1002/jcc.10360

Cited by 29 publications

(40 citation statements)

References 47 publications

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“…Given the ionization energies of the two possible product radicals (ionization energies of allylic and vinylic C 4 H 7 radicals are B7.9 (ref. 23) and 8.4 eV, respectively, with the latter value calculated at the CBS-QB3 level of theory), and the fact that H migration cannot occur in the energized radical product as established for similar systems (propene and isoprene) 15 , we can confidently rule out the possible detection of radical products stemming from the abstraction directly at the double bond. The distributions presented here, and their changes with collision energies, correspond to reaction at the allylic sites only.…”

Section: Resultssupporting

confidence: 57%

“…State-selected HCl measurements have not shown a distinct feature of addition-elimination in the product distributions 13 . Quantum chemical calculations of reaction potential energy surfaces (PESs) have been unable to corroborate the additionelimination mechanism 14,15 . Recently, we have investigated the reactions of chlorine atoms with various alkenes such as butene isomers, 1-pentene and various hexene isomers using a crossed-beam apparatus coupled to DC slice ion imaging 16,17 We have found that the scattering distributions reflect the competition between direct H abstraction and Cl addition-HCl elimination.…”

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confidence: 99%

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Roaming dynamics in radical addition–elimination reactions

et al. 2014

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Radical addition-elimination reactions are a major pathway for transformation of unsaturated hydrocarbons. In the gas phase, these reactions involve formation of a transient strongly bound intermediate. However, the detailed mechanism and dynamics for these reactions remain unclear. Here we show, for reaction of chlorine atoms with butenes, that the Cl addition-HCl elimination pathway occurs from an abstraction-like Cl-H-C geometry rather than a conventional three-centre or four-centre transition state. Furthermore, access to this geometry is attained by roaming excursions of the Cl atom from the initially formed adduct. In effect, the alkene p cloud serves to capture the Cl atom and hold it, allowing many subsequent opportunities for the energized intermediate to find a suitable approach to the abstraction geometry. These bimolecular roaming reactions are closely related to the roaming radical dynamics recently discovered to play an important role in unimolecular reactions.

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Section: Resultssupporting

confidence: 57%

mentioning

confidence: 99%

Roaming dynamics in radical addition–elimination reactions

et al. 2014

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“…Reaction (1), and related reactions in larger alkenes, therefore present an opportunity to study the competition between direct and indirect reaction pathways. 6,[8][9][10] No transition state (TS) leads straight from the chloropropyl potential energy (PE) wells to HCl products, 7 but a TS has been suggested to connect these deep PE wells with the direct abstraction pathway. Approximately half of the HCl molecules from reaction (1) form with one quantum of vibrational excitation, corresponding to 34.5 kJ mol -1 of internal energy.…”

Section: Introductionmentioning

confidence: 99%

Computational Study of Competition between Direct Abstraction and Addition–Elimination in the Reaction of Cl Atoms with Propene

et al. 2015

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Quasi-classical trajectory calculations on a newly constructed and full-dimensionality potential energy surface (PES) examine the dynamics of the reaction of Cl atoms with propene. The PES is an empirical valence bond (EVB) fit to high-level ab initio energies and incorporates deep potential energy wells for the 1-chloropropyl and 2-chloropropyl radicals, a direct H-atom abstraction route to HCl + allyl radical (CH2CHCH2·) products (∆ 298 = 63.1 kJ mol -1 ), and a pathway connecting these regions. In total, 94000 successful reactive trajectories were used to compute distributions of angular scattering and HCl vibrational and rotational level populations. These measures of the reaction dynamics agree satisfactorily with available experimental data. The dominant reaction pathway is direct abstraction of a hydrogen atom from the methyl group of propene occurring in under 500 fs. Fewer than 10% of trajectories follow an addition-elimination route via the two isomeric chloropropyl radicals. Large amplitude motions of the Cl about the propene molecular framework couple the addition intermediates to the direct abstraction pathway. The EVB method provides a good description of the complicated PES for the Cl + propene reaction despite fitting to a limited number of ab initio points, with the further advantage that dynamics specific to certain mechanisms can be studied in isolation by switching off coupling terms in the EVB matrix connecting different regions of the PES.

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“…For example, cOH prefers to abstract the hydrogen atoms of propene while cCl prefers to add to the unsaturated bond. [13][14][15] Theoretical research on reaction of acrylonitrile with cOH demonstrates that addition is the dominant reaction over abstraction at temperatures <1000 K, but that abstraction is dominant over addition at higher temperatures. 16 Thus, acrylonitrile reaction with cCl may also follow the addition and H-abstraction mechanism.…”

Section: -5mentioning

confidence: 99%

“…[11][12][13] The favored pathway for reaction of an unsaturated organic compound (such as CH 2 ]CHR) with cCl is not always the same as that with cOH. For example, cOH prefers to abstract the hydrogen atoms of propene while cCl prefers to add to the unsaturated bond.…”

Section: -5mentioning

confidence: 99%