1
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Jung J, Shin J, Dzhaparova A, Park JK, Lim M. Photoexcitation dynamics of bromodiphenyl ethers in acetonitrile-d 3 studied by femtosecond time-resolved infrared spectroscopy. Phys Chem Chem Phys 2022; 24:9203-9212. [PMID: 35388852 DOI: 10.1039/d2cp00063f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The efficient decomposition of polybrominated diphenyl ethers (PBDEs), onetime prevalent flame retardants, is central to the reduction of their harmful effects on human health. PBDE photodecomposition is a promising method, but its mechanism and products are not well understood. The photoexcitation dynamics of 3- and 4-bromodiphenyl ethers (BDE-2 and BDE-3) in CD3CN were studied from 0.3 ps to 10 μs using time-resolved infrared spectroscopy. An excitation at 267 nm dissociated the Br atom from BDE-2 and BDE-3 within 0.3 ps and 14 ± 3 ps, respectively, producing a radical compound (R) and a Br atom. About 85% of R formed an intermediate (IM) that weakly interacted with the Br atom and the surrounding CD3CN solvent in 7-12 ps. The remaining R separated from the dissociated Br and underwent slow geminate rebinding (GR) with Br within 35 to 54 ns. The IM competitively engaged in GR with the interacting Br in 40-60 ps or formed CD3CN-bound radical compounds (RS) in 100-130 ps. The RS further degraded via either the dissociation of CD3-producing a cyano-bound diphenyl ether (DE) in 150 or 550 ns-or the deuterium abstraction of CD3CN in 180 or 430 ns-producing a deuterated DE. Overall, 33 ± 3 (22 ± 3)% of the photoexcited BDE-2 (BDE-3) decomposed in CD3CN under 267 nm excitation. Efficient binding of the CD3CN solvent to R deterred the yield-diminishing GR and slowed the rate of product formation. The observed photoexcitation dynamics of BDE suggest methods for the efficient decomposition of PBDE.
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Affiliation(s)
- Jisik Jung
- Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea.
| | - Juhyang Shin
- Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea.
| | - Alina Dzhaparova
- Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea.
| | - Jin Kyoon Park
- Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea.
| | - Manho Lim
- Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 46241, Korea.
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2
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Cascarini FJJ, Hornung B, Quinn MS, Robertson PA, Orr-Ewing AJ. Collision Energy Dependence of the Competing Mechanisms of Reaction of Chlorine Atoms with Propene. J Phys Chem A 2019; 123:2679-2686. [DOI: 10.1021/acs.jpca.9b01370] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Balázs Hornung
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, United Kingdom
| | - Mitchell S. Quinn
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, United Kingdom
| | - Patrick A. Robertson
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, United Kingdom
| | - Andrew J. Orr-Ewing
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, United Kingdom
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3
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Abstract
The dynamics of chemical reactions in liquid solutions are now amenable to direct study using ultrafast laser spectroscopy techniques and advances in computer simulation methods. The surrounding solvent affects the chemical reaction dynamics in numerous ways, which include: (i) formation of complexes between reactants and solvent molecules; (ii) modifications to transition state energies and structures relative to the reactants and products; (iii) coupling between the motions of the reacting molecules and the solvent modes, and exchange of energy; (iv) solvent caging of reactants and products; and (v) structural changes to the solvation shells in response to the changing chemical identity of the solutes, on timescales which may be slower than the reactive events. This article reviews progress in the study of bimolecular chemical reaction dynamics in solution, concentrating on reactions which occur on ground electronic states. It illustrates this progress with reference to recent experimental and computational studies, and considers how the various ways in which a solvent affects the chemical reaction dynamics can be unravelled. Implications are considered for research in fields such as mechanistic synthetic chemistry.
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Affiliation(s)
- Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
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4
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Shin JY, Shaloski MA, Crim FF, Case AS. First Evidence of Vibrationally Driven Bimolecular Reactions in Solution: Reactions of Br Atoms with Dimethylsulfoxide and Methanol. J Phys Chem B 2017; 121:2486-2494. [DOI: 10.1021/acs.jpcb.7b00035] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jae Yoon Shin
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Michael A. Shaloski
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - F. Fleming Crim
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Amanda S. Case
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
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5
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Shin JY, Case AS, Crim FF. Comparative Study of Cl-Atom Reactions in Solution Using Time-Resolved Vibrational Spectroscopy. J Phys Chem B 2016; 120:3920-31. [DOI: 10.1021/acs.jpcb.6b01765] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jae Yoon Shin
- Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
| | - Amanda S. Case
- Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
| | - F. Fleming Crim
- Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
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6
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Carpenter BK, Harvey JN, Orr-Ewing AJ. The Study of Reactive Intermediates in Condensed Phases. J Am Chem Soc 2016; 138:4695-705. [DOI: 10.1021/jacs.6b01761] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Barry K. Carpenter
- School
of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, U.K
| | - Jeremy N. Harvey
- Department
of Chemistry, KU Leuven, Celestijnen Laan 200F, B-3001 Heverlee, Belgium
| | - Andrew J. Orr-Ewing
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
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7
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Preston TJ, Hornung B, Pandit S, Harvey JN, Orr-Ewing AJ. Dynamical Effects and Product Distributions in Simulated CN + Methane Reactions. J Phys Chem A 2016; 120:4672-82. [DOI: 10.1021/acs.jpca.5b09487] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Thomas J. Preston
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Balázs Hornung
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Shubhrangshu Pandit
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
| | - Jeremy N. Harvey
- Department
of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven (Heverlee), Belgium
| | - Andrew J. Orr-Ewing
- School
of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K
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8
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Hornung B, Preston TJ, Pandit S, Harvey JN, Orr-Ewing AJ. Computational Study of Competition between Direct Abstraction and Addition-Elimination in the Reaction of Cl Atoms with Propene. J Phys Chem A 2015; 119:9452-64. [PMID: 26288318 DOI: 10.1021/acs.jpca.5b07052] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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 (Δ(r)H(298K)(⊖) = −63.1 kJ mol(-1)), and a pathway connecting these regions. In total, 94 000 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. Less 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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Affiliation(s)
- Balázs Hornung
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Thomas J Preston
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Shubhrangshu Pandit
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Jeremy N Harvey
- Department of Chemistry, KU Leuven , Celestijnenlaan 200F, B-3001 Leuven (Heverlee), Belgium
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom
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9
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Dunning GT, Preston TJ, Greaves SJ, Greetham GM, Clark IP, Orr-Ewing AJ. Vibrational Excitation of Both Products of the Reaction of CN Radicals with Acetone in Solution. J Phys Chem A 2015; 119:12090-101. [PMID: 26192334 PMCID: PMC4685429 DOI: 10.1021/acs.jpca.5b05624] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Transient electronic and vibrational absorption spectroscopy unravel the mechanisms and dynamics of bimolecular reactions of CN radicals with acetone in deuterated chloroform solutions. The CN radicals are produced by ultrafast ultraviolet photolysis of dissolved ICN. Two reactive forms of CN radicals are distinguished by their electronic absorption bands: "free" (uncomplexed) CN radicals, and "solvated" CN radicals that are complexed with solvent molecules. The lifetimes of the free CN radicals are limited to a few picoseconds following their photolytic production because of geminate recombination to ICN and INC, complexation with CDCl3 molecules, and reaction with acetone. The acetone reaction occurs with a rate coefficient of (8.0 ± 0.5) × 10(10) M(-1) s(-1) and transient vibrational spectra in the C═N and C═O stretching regions reveal that both the nascent HCN and 2-oxopropyl (CH3C(O)CH2) radical products are vibrationally excited. The rate coefficient for the reaction of solvated CN with acetone is 40 times slower than for free CN, with a rate coefficient of (2.0 ± 0.9) × 10(9) M(-1) s(-1) obtained from the rise in the HCN product v1(C═N stretch) IR absorption band. Evidence is also presented for CN complexes with acetone that are more strongly bound than the CN-CDCl3 complexes because of CN interactions with the carbonyl group. The rates of reactions of these more strongly associated radicals are slower still.
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Affiliation(s)
- Greg T Dunning
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K
| | - Thomas J Preston
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K
| | - Stuart J Greaves
- School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K
| | - Gregory M Greetham
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Harwell Oxford, Didcot, Oxfordshire OX11 0QX, U.K
| | - Ian P Clark
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory , Harwell Oxford, Didcot, Oxfordshire OX11 0QX, U.K
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K
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10
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Glowacki DR, Orr-Ewing AJ, Harvey JN. Non-equilibrium reaction and relaxation dynamics in a strongly interacting explicit solvent: F + CD3CN treated with a parallel multi-state EVB model. J Chem Phys 2015; 143:044120. [DOI: 10.1063/1.4926996] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- David R. Glowacki
- School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
- Department of Computer Science, University of Bristol, Bristol BS8 1UB, United Kingdom
- PULSE Institute and Department of Chemistry, Stanford University, Stanford, California 94305, USA
- SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | | | - Jeremy N. Harvey
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Heverlee, Belgium
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11
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Affiliation(s)
- Andrew J. Orr-Ewing
- School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom;
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12
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Dunning GT, Murdock D, Greetham GM, Clark IP, Orr-Ewing AJ. Solvent response to fluorine-atom reaction dynamics in liquid acetonitrile. Phys Chem Chem Phys 2015; 17:9465-70. [DOI: 10.1039/c5cp00774g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Solvent restructuring and vibrational cooling follow exothermic fluorine-atom reactions in acetonitrile.
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Affiliation(s)
- G. T. Dunning
- School of Chemistry
- University of Bristol
- Cantock's Close
- Bristol BS8 1TS
- UK
| | - D. Murdock
- School of Chemistry
- University of Bristol
- Cantock's Close
- Bristol BS8 1TS
- UK
| | - G. M. Greetham
- Central Laser Facility
- Research Complex at Harwell
- Science and Technology Facilities Council
- Rutherford Appleton Laboratory
- Oxfordshire
| | - I. P. Clark
- Central Laser Facility
- Research Complex at Harwell
- Science and Technology Facilities Council
- Rutherford Appleton Laboratory
- Oxfordshire
| | - A. J. Orr-Ewing
- School of Chemistry
- University of Bristol
- Cantock's Close
- Bristol BS8 1TS
- UK
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13
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Orr-Ewing AJ. Perspective: Bimolecular chemical reaction dynamics in liquids. J Chem Phys 2014; 140:090901. [PMID: 24606343 DOI: 10.1063/1.4866761] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Bimolecular reactions in the gas phase exhibit rich and varied dynamical behaviour, but whether a profound knowledge of the mechanisms of isolated reactive collisions can usefully inform our understanding of reactions in liquid solutions remains an open question. The fluctuating environment in a liquid may significantly alter the motions of the reacting particles and the flow of energy into the reaction products after a transition state has been crossed. Recent experimental and computational studies of exothermic reactions of CN radicals with organic molecules indicate that many features of the gas-phase dynamics are retained in solution. However, observed differences may also provide information on the ways in which a solvent modifies fundamental chemical mechanisms. This perspective examines progress in the use of time-resolved infra-red spectroscopy to study reaction dynamics in liquids, discusses how existing theories can guide the interpretation of experimental data, and suggests future challenges for this field of research.
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Affiliation(s)
- Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
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14
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Joalland B, Shi Y, Estillore AD, Kamasah A, Mebel AM, Suits AG. Dynamics of chlorine atom reactions with hydrocarbons: insights from imaging the radical product in crossed beams. J Phys Chem A 2014; 118:9281-95. [PMID: 25076054 DOI: 10.1021/jp504804n] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a comprehensive overview of our ongoing studies applying dc slice imaging in crossed molecular beams to probe the dynamics of chlorine atom reactions with polyatomic hydrocarbons. Our approach consists in measuring the full velocity-flux contour maps of the radical products using vacuum ultraviolet "soft" photoionization at 157 nm. Our overall goal is to extend the range of chemical dynamics investigations from simple triatomic or tetraatomic molecules to systematic investigations of a sequence of isomers or a homologous series of reactants of intermediate size. These experimental investigations are augmented by high-level ab initio calculations which, taken together, reveal trends in product energy and angular momentum partitioning and offer deep insight into the reaction mechanisms as a function of structure, bonding patterns, and kinematics. We explore these issues in alkanes, for which only direct reactive encounters are found, and in unsaturated hydrocarbons, for which an addition-elimination mechanism competes with direct abstraction. The results for alkene addition-elimination in particular suggest a new view of these reactions: The only pathway to HCl elimination is accessed by means of roaming excursions of the Cl atom from the strongly bound adduct.
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Affiliation(s)
- Baptiste Joalland
- Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States
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15
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Preston TJ, Dunning GT, Orr-Ewing AJ, Vázquez SA. Direct and Indirect Hydrogen Abstraction in Cl + Alkene Reactions. J Phys Chem A 2014; 118:5595-607. [DOI: 10.1021/jp5042734] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Thomas J. Preston
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom
| | - Greg T. Dunning
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom
| | - Andrew J. Orr-Ewing
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom
| | - Saulo A. Vázquez
- Departamento de Química
Física and Centro Singular de Investigación Química
Biológica y Materiales Moleculares, Campus Vida, Universidad de Santiago de Compostela, 15782 Santiago
de Compostela, Spain
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16
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Joalland B, Shi Y, Kamasah A, Suits AG, Mebel AM. Roaming dynamics in radical addition–elimination reactions. Nat Commun 2014; 5:4064. [DOI: 10.1038/ncomms5064] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 05/06/2014] [Indexed: 11/09/2022] Open
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17
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Abou-Chahine F, Preston TJ, Dunning GT, Orr-Ewing AJ, Greetham GM, Clark IP, Towrie M, Reid SA. Photoisomerization and Photoinduced Reactions in Liquid CCl4 and CHCl3. J Phys Chem A 2013; 117:13388-98. [DOI: 10.1021/jp406687x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Fawzi Abou-Chahine
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, U.K
| | - Thomas J. Preston
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, U.K
| | - Greg T. Dunning
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, U.K
| | - Andrew J. Orr-Ewing
- School of Chemistry, University of Bristol, Cantock’s
Close, Bristol BS8 1TS, U.K
| | - Gregory M. Greetham
- Central Laser Facility,
Research Complex
at Harwell, Science and Technology Facilities Council, Rutherford
Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, U.K
| | - Ian P. Clark
- Central Laser Facility,
Research Complex
at Harwell, Science and Technology Facilities Council, Rutherford
Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, U.K
| | - Mike Towrie
- Central Laser Facility,
Research Complex
at Harwell, Science and Technology Facilities Council, Rutherford
Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0QX, U.K
| | - Scott A. Reid
- Department of Chemistry, Marquette University, 535 North 14th
Street, Milwaukee, Wisconsin 53233, United States
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18
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Harris SJ, Murdock D, Zhang Y, Oliver TAA, Grubb MP, Orr-Ewing AJ, Greetham GM, Clark IP, Towrie M, Bradforth SE, Ashfold MNR. Comparing molecular photofragmentation dynamics in the gas and liquid phases. Phys Chem Chem Phys 2013; 15:6567-82. [PMID: 23552482 DOI: 10.1039/c3cp50756d] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This article explores the extent to which insights gleaned from detailed studies of molecular photodissociations in the gas phase (i.e. under isolated molecule conditions) can inform our understanding of the corresponding photofragmentation processes in solution. Systems selected for comparison include a thiophenol (p-methylthiophenol), a thioanisole (p-methylthioanisole) and phenol, in vacuum and in cyclohexane solution. UV excitation in the gas phase results in RX-Y (X = O, S; Y = H, CH3) bond fission in all cases, but over timescales that vary by ~4 orders of magnitude - all of which behaviours can be rationalised on the basis of the relevant bound and dissociative excited state potential energy surfaces (PESs) accessed by UV photoexcitation, and of the conical intersections that facilitate radiationless transfer between these PESs. Time-resolved UV pump-broadband UV/visible probe and/or UV pump-broadband IR probe studies of the corresponding systems in cyclohexane solution reveal additional processes that are unique to the condensed phase. Thus, for example, the data clearly reveal evidence of (i) vibrational relaxation of the photoexcited molecules prior to their dissociation and of the radical fragments formed upon X-Y bond fission, and (ii) geminate recombination of the RX and Y products (leading to reformation of the ground state parent and/or isomeric adducts). Nonetheless, the data also show that, in each case, the characteristics (and the timescale) of the initial bond fission process that occurs under isolated molecule conditions are barely changed by the presence of a weakly interacting solvent like cyclohexane. These condensed phase studies are then extended to an ether analogue of phenol (allyl phenyl ether), wherein UV photo-induced RO-allyl bond fission constitutes the first step of a photo-Claisen rearrangement.
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Affiliation(s)
- Stephanie J Harris
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK
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