Vibrationally resolved dynamics of the reaction of Cl atoms with 2,3-dimethylbut-2-ene in chlorinated solvents

Abou‐Chahine, Fawzi; Greaves, Stuart J.; Dunning, Greg T.; Orr-Ewing, Andrew J.; Greetham, Gregory M.; Clark, Ian P.; Towrie, Michael

doi:10.1039/c2sc21267f

Cited by 18 publications

(71 citation statements)

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“…We previously reported time-resolved IR studies of this reaction in solution, 19 for which we observed formation of HCl(v=0 and 1) products, indicative of direct abstraction dynamics.…”

Section: Comparison Of Reaction Rates and Mechanismsmentioning

confidence: 99%

“…We also undertook time-resolved vibrational spectroscopy studies of all the solutions, but these were less informative than the electronic spectroscopy data, with the exception of the 2,3-dimethylbut-2-ene system which was the focus of an earlier publication. 19 The transient spectral features observed in infra-red absorption measurements for 1,5-hexadiene can all be assigned to radical cation pathways. 29 …”

Section: Introductionmentioning

confidence: 99%

“…19 Addition of a Cl atom followed by solvent stabilization of the adduct might be expected to dominate such reactions of unsaturated solutes, based on observations of the pressure dependence of the mechanisms of related gas-phase reactions. However, the reaction of Cl atoms with 2,3-dimethylbut-2-ene demonstrates that abstraction pathways can compete.…”

Section: Introductionmentioning

confidence: 99%

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Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Abou‐Chahine¹,

Preston²,

Dunning³

et al. 2013

J. Phys. Chem. A

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Transient absorption spectroscopy is used to follow the reactive intermediates involved in the first steps in the photochemistry initiated by ultraviolet (266-nm wavelength) excitation of solutions of 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in carbon tetrachloride or chloroform. Ultraviolet and visible bands centred close to 330 nm and 500 nm in both solvents are assigned respectively to a charge transfer band of Cl-solvent complexes, and the strong absorption band of a higher energy isomeric form of the solvent molecules (iso-CCl3-Cl or iso-CHCl2-Cl). These assignments are supported by calculations of electronic excitation energies. The isomeric forms have significant contributions to their structures from charge-separated resonance forms, and offer a re-interpretation of previous assignments of the carriers of the visible bands that were based on pulsed radiolysis experiments. Kinetic analysis demonstrates that the isomeric forms are produced via the Cl-solvent complexes.Addition of the unsaturated hydrocarbons provides a reactive loss channel for the Cl-solvent complexes, and reaction radii and bimolecular rate coefficients are derived from analysis using a Smoluchowski theory model. For reactions of Cl with 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in CCl4, rate coefficients at 294 K are, respectively, (8.6  0.8)  10 9 M -1 s -1 , (9.5  1.6)  10 9 M -1 s -1 and (1.7  0.1)  10 10 M -1 s -1 . The larger reaction radius and rate coefficient for 2,3-dimethylbut-2-ene are interpreted as evidence for an H-atom abstraction channel that competes effectively with the channel involving addition of a Cl atom to a C=C bond. However, the addition mechanism appears to dominate the reactions of 1,5-hexadiene and isoprene. Two-photon excited CCl4 or CHCl3 can also ionize the diene or alkene solute.

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“…We previously reported time-resolved IR studies of this reaction in solution, 19 for which we observed formation of HCl(v=0 and 1) products, indicative of direct abstraction dynamics.…”

Section: Comparison Of Reaction Rates and Mechanismsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Abou‐Chahine¹,

Preston²,

Dunning³

et al. 2013

J. Phys. Chem. A

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“…6,[34][35][36][37][38] The last decade or so has seen a number of attempts by a range of workers to efficiently and accurately simulate chemical reaction dynamics in condensed-phase environments using multistate molecular mechanics and multi-state empirical valence bond (MS-EVB) approaches. 19,[39][40][41][42][43][44][45][46][47][48][49] Such approaches represent important molecular configurations using diabatic valence bond states, which are coupled using any of a wide range of schemes.…”

Section: Introductionmentioning

confidence: 99%

Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model

Glowacki

Orr-Ewing

Harvey

2015

The Journal of Chemical Physics

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We describe a parallelized linear-scaling computational framework developed to implement arbitrarily large multi-state empirical valence bond (MS-EVB) calculations within CHARMM and TINKER. Forces are obtained using the Hellmann-Feynman relationship, giving continuous gradients, and good energy conservation. Utilizing multi-dimensional Gaussian coupling elements fit to explicitly correlated coupled cluster theory, we built a 64-state MS-EVB model designed to study the F + CD3CN → DF + CD2CN reaction in CD3CN solvent (recently reported in Dunning et al. [Science 347(6221), 530 (2015)]). This approach allows us to build a reactive potential energy surface whose balanced accuracy and efficiency considerably surpass what we could achieve otherwise. We ran molecular dynamics simulations to examine a range of observables which follow in the wake of the reactive event: energy deposition in the nascent reaction products, vibrational relaxation rates of excited DF in CD3CN solvent, equilibrium power spectra of DF in CD3CN, and time dependent spectral shifts associated with relaxation of the nascent DF. Many of our results are in good agreement with time-resolved experimental observations, providing evidence for the accuracy of our MS-EVB framework in treating both the solute and solute/solvent interactions. The simulations provide additional insight into the dynamics at sub-picosecond time scales that are difficult to resolve experimentally. In particular, the simulations show that (immediately following deuterium abstraction) the nascent DF finds itself in a non-equilibrium regime in two different respects: (1) it is highly vibrationally excited, with ∼23 kcal mol−1 localized in the stretch and (2) its post-reaction solvation environment, in which it is not yet hydrogen-bonded to CD3CN solvent molecules, is intermediate between the non-interacting gas-phase limit and the solution-phase equilibrium limit. Vibrational relaxation of the nascent DF results in a spectral blue shift, while relaxation of the post-reaction solvation environment results in a red shift. These two competing effects mean that the post-reaction relaxation profile is distinct from what is observed when Franck-Condon vibrational excitation of DF occurs within a microsolvation environment initially at equilibrium. Our conclusions, along with the theoretical and parallel software framework presented in this paper, should be more broadly applicable to a range of complex reactive systems.

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“…These reactions play an important role in the oxidation of volatile organic compounds in marine boundary layers and the Polar regions [2][3][4] , the burning of hazardous waste 5 and possibly the aging of organic aerosols by heterogeneous processes 6 . In these bimolecular reactions that have become key in studying polyatomic reaction dynamics both in the gas phase 7 and in solution 8 , HCl formation is a major pathway for which additionelimination competes with direct abstraction:…”

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confidence: 99%

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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Vibrationally resolved dynamics of the reaction of Cl atoms with 2,3-dimethylbut-2-ene in chlorinated solvents

Cited by 18 publications

References 50 publications

Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model

Roaming dynamics in radical addition–elimination reactions

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Vibrationally resolved dynamics of the reaction of Cl atoms with 2,3-dimethylbut-2-ene in chlorinated solvents

Cited by 18 publications

References 50 publications

Photoisomerization and Photoinduced Reactions in Liquid CCl4 and CHCl3

Photoisomerization and Photoinduced Reactions in Liquid CCl4 and CHCl3

Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model

Roaming dynamics in radical addition–elimination reactions

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Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃

Photoisomerization and Photoinduced Reactions in Liquid CCl₄ and CHCl₃