Direct Observation of Tetrahydrofuranyl and Tetrahydropyranyl Peroxy Radicals via Cavity Ring-Down Spectroscopy

Telfah, Hamzeh; Reza, Asmaul; Alam, Jahangir; Paul, Anam C.; Liu, Jinjun

doi:10.1021/acs.jpclett.8b01721

Cited by 10 publications

(7 citation statements)

References 28 publications

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“…The latter substituent factor is derived from Atkinson 51 assuming the same reduction as for F(−CH 2 −) when H-abstraction from an ether group is by Cl • compared to • OH. 50 The SAR-predicted rate coefficient for tetrahydropyran + Cl • → R • + HCl (4.78 × 10 −10 molecules cm −3 ) is within a factor of approximately 2 compared with the measurements of Giri and Roscoe 52 and Alwe et al, 53 and the distribution of R • is dominated by α radicals, which is consistent with the ab initio calculations of Ballesteros et al 45 On a per-C−H bond basis, the branching ratio for tetrahydropyranyl radicals is approximated as α/β/γ = 0.76:0.16:0.08, which is similar to the distribution in Tran et al 27 The results are also consistent with the spectroscopic results from Telfah et al, 38 in which ∼80% of the peroxy radicals were α-ROO • . Using a different method of approximation, the α radical remains dominant in Habstraction reactions from tetrahydropyran by • OH.…”

Section: Experimental and Computational Approachsupporting

confidence: 89%

“…While several experimental and computational studies on cyclohexane oxidation exist at temperatures below 1000 K, ,− a limited number of combustion-relevant studies exist for tetrahydropyran. Telfah et al measured cavity ring-down spectra of the Ã ← X̃ electronic transitions of tetrahydropyranylperoxy radicals, produced using Cl-initiated oxidation, to resolve the geometries of structural conformers. Quantum chemical calculations were conducted to determine Franck–Condon factors for vibronic transitions and indicated that ∼80% of the peroxy radicals are conformers of α-tetrahydropyranylperoxy, the majority of which are axial.…”

Section: Introductionmentioning

confidence: 99%

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Influence of the Ether Functional Group on Ketohydroperoxide Formation in Cyclic Hydrocarbons: Tetrahydropyran and Cyclohexane

Davis¹,

Koritzke²,

Caravan

et al. 2019

J. Phys. Chem. A

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Photolytically initiated oxidation experiments were conducted on cyclohexane and tetrahydropyran using multiplexed photoionization mass spectrometry to assess the impact of the ether functional group in the latter species on reaction mechanisms relevant to autoignition. Pseudo-firstorder conditions, with [O 2 ] 0 :[R • ] 0 > 2000, were used to ensure that R • + O 2 → products were the dominant reactions. Quasi-continuous, tunable vacuum ultraviolet light from a synchrotron was employed over the range 8.0−11.0 eV to measure photoionization spectra of the products at two pressures (10 and 1520 Torr) and three temperatures (500, 600, and 700 K). Photoionization spectra of ketohydroperoxides were measured in both species and were qualitatively identical, within the limit of experimental noise, to those of analogous species formed in n-butane oxidation. However, differences were noted in the temperature dependence of ketohydroperoxide formation between the two species. Whereas the yield from cyclohexane is evident up to 700 K, ketohydroperoxides in tetrahydropyran were not detected above 650 K. The difference indicates that reaction mechanisms change due to the ether group, likely affecting the requisite • QOOH + O 2 addition step. Branching fractions of nine species from tetrahydropyran were quantified with the objective of determining the role of ring-opening reactions in diminishing ketohydroperoxide. The results indicate that products formed from unimolecular decomposition of R • and • QOOH radicals via concerted C−C and C−O β-scission are pronounced in tetrahydropyran and are insignificant in cyclohexane oxidation. The main conclusion drawn is that, under the conditions herein, ring-opening pathways reduce the already low steady-state concentration of • QOOH, which in the case of tetrahydropyran prevents • QOOH + O 2 reactions necessary for ketohydroperoxide formation. Carbon balance calculations reveal that products from ring opening of both R • and • QOOH, at 700 K, account for >70% at 10 Torr and >55% at 1520 Torr. Three pathways are confirmed to contribute to the depletion of • QOOH in tetrahydropyran including (i) γ-• QOOH → pentanedial + • OH, (ii) γ-• QOOH → vinyl formate + ethene + • OH, and (iii) γ-• QOOH → 3-butenal + formaldehyde + • OH. Analogous mechanisms in cyclohexane oxidation leading to similar intermediates are compared and, on the basis of mass spectral results, confirm that no such ringopening reactions occur. The implication from the comparison to cyclohexane is that the ether group in tetrahydropyran increases the propensity for ring-opening reactions and inhibits the formation of ketohydroperoxide isomers that precede chainbranching. On the contrary, the absence of such reactions in cyclohexane enables ketohydroperoxide formation up to 700 K and perhaps higher temperature.

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Section: Experimental and Computational Approachsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Influence of the Ether Functional Group on Ketohydroperoxide Formation in Cyclic Hydrocarbons: Tetrahydropyran and Cyclohexane

Davis¹,

Koritzke²,

Caravan

et al. 2019

J. Phys. Chem. A

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“…Those papers that emphasize experimental work include ones that focus on spectroscopic detection of radicals using infrared spectroscopy in He nanodroplets, visible cavity ring-down spectroscopy, tunable VUV photoelectron–photoion coincidence methods, and tabletop tunable VUV . Kinetic studies include those formed by model biofuels , and site-specific attack of hydrocarbons .…”

mentioning

confidence: 99%

Virtual Issue on Combustion Chemistry

Guo¹,

Yang

Zwier

2020

J. Phys. Chem. A

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A lthough combustion chemistry has been an important research topic since the early days of Physical Chemistry, our understanding of the chemical species involved in combustion and their reactivity has been an ongoing challenge that stimulates intense current interest. The range of combustion fuels continues to diversify, including everything from biofuels to metal nanoparticles. In this Virtual Issue, we have chosen articles that represent the wide scope of the field. Furthermore, recent advances in both experimental techniques and theoretical algorithms have greatly extended our ability to directly interrogate this complex chemistry and address fundamental questions arising from this area of research. In total, we collect 30 examples of publications that have appeared in The Journal of Physical Chemistry over the time period from 2016 to 2019. These representative publications not only address questions directly related to combustion but also tackle issues fundamental in nature.Those papers that emphasize experimental work include ones that focus on spectroscopic detection of radicals using infrared spectroscopy in He nanodroplets, 1 visible cavity ring-down spectroscopy, 2 tunable VUV photoelectron−photoion coincidence methods, 3 and tabletop tunable VUV. 4 Kinetic studies include those formed by model biofuels 5,6 and site-specific attack of hydrocarbons. 7 One of the continuing puzzles in combustion models is the chemistry leading to soot formation. The work of Johansson et al. 8 particularly highlights the critical need for foundational data used to quantify soot precursors in flames. Several studies flesh out new combustion chemistry, whether involving hydrocarbon oxidation, 9 O 2 ( 1 Σ g + ) chemistry, 10 or the more exotic chemistry involved in silane oxidation. 11 In papers that extend beyond traditional notions of combustion, there are those that describe work on catalyzed combustion of methane 12 and toluene 13 and solid-state oxygen sources for chemical looping combustion. 14 Finally, three of the publications in this Virtual Issue take up the subject of nanoparticle-enhanced combustion, investigating Al nanoparticles 15,16 and Ni-CeO x hybrid nanoparticles. 17 Theoretical papers also cover many topics, ranging from accurate 18,19 and approximate 20 studies of molecular properties, interaction potential energy surfaces, 21−23 transition state theory calculations of rate coefficients, 24 and master equation simulations 25 to sensitivity of kinetic models. 26 There are also theoretical studies of combustion reactions in nonconventional environments 27 and with heavy fuel molecules 28,29 and hypergolic propellants. 30 Many of the selected experimental papers also have a computational component and they benefit from experimental-theoretical synergy.The selection for this Virtual Issue is by no means complete or unique. However, it is our hope that it will give a representative snapshot of the field at this point in time. We expect that future research in this fertile field of research will further advanc...

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“…The CRD apparatus used in the present work is similar to the room-temperature CRD setup described in our previous papers 62,78 , except that the free radicals are produced by laser ablation under jet-cooled conditions as described in the main text. CRD mirrors…”

Section: Experimental (Cavity Ring-down Spectroscopy)mentioning

confidence: 99%

Laser spectroscopy investigations of jet-cooled metal-containing free radicals.

Paul¹

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Direct Observation of Tetrahydrofuranyl and Tetrahydropyranyl Peroxy Radicals via Cavity Ring-Down Spectroscopy

Cited by 10 publications

References 28 publications

Influence of the Ether Functional Group on Ketohydroperoxide Formation in Cyclic Hydrocarbons: Tetrahydropyran and Cyclohexane

Influence of the Ether Functional Group on Ketohydroperoxide Formation in Cyclic Hydrocarbons: Tetrahydropyran and Cyclohexane

Virtual Issue on Combustion Chemistry

Laser spectroscopy investigations of jet-cooled metal-containing free radicals.

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