The 1,5-H-shift in 1-butoxy: A case study in the rigorous implementation of transition state theory for a multirotamer system

Vereecken, Luc; Peeters, Jozef

doi:10.1063/1.1597479

Cited by 124 publications

(155 citation statements)

References 39 publications

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“…We calculate the rate constants of the H-shift reactions using multiconformer transition state theory (MC-TST) (53)(54)(55)(56). The MC-TST expression for a rate constant is given by the following:…”

Section: Resultsmentioning

confidence: 99%

Atmospheric autoxidation is increasingly important in urban and suburban North America

Praske

Otkjær

Crounse

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

176

310

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Gas-phase autoxidation-regenerative peroxy radical formation following intramolecular hydrogen shifts-is known to be important in the combustion of organic materials. The relevance of this chemistry in the oxidation of organics in the atmosphere has received less attention due, in part, to the lack of kinetic data at relevant temperatures. Here, we combine computational and experimental approaches to investigate the rate of autoxidation for organic peroxy radicals (RO 2 ) produced in the oxidation of a prototypical atmospheric pollutant, n-hexane. We find that the reaction rate depends critically on the molecular configuration of the RO 2 radical undergoing hydrogen transfer (H-shift). RO 2 H-shift rate coefficients via transition states involving six-and seven-membered rings (1,5 and 1,6 H-shifts, respectively) of α-OH hydrogens (HOC-H) formed in this system are of order 0.1 s −1 at 296 K, while the 1,4 H-shift is calculated to be orders of magnitude slower. Consistent with H-shift reactions over a substantial energetic barrier, we find that the rate coefficients of these reactions increase rapidly with temperature and exhibit a large, primary, kinetic isotope effect. The observed H-shift rate coefficients are sufficiently fast that, as a result of ongoing NO x emission reductions, autoxidation is now competing with bimolecular chemistry even in the most polluted North American cities, particularly during summer afternoons when NO levels are low and temperatures are elevated.atmospheric chemistry | air pollution | autoxidation

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Section: Resultsmentioning

confidence: 99%

Atmospheric autoxidation is increasingly important in urban and suburban North America

Praske

Otkjær

Crounse

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

176

310

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“…Conversely, the same quantities show larger differences when comparing the

M 8_{aug ‐ pcseg ‐ 1}

and

M 8_{aug ‐ pcseg ‐ 1}^{aug ‐ pcseg ‐ 2}

levels of theory. The reason for carefully monitoring such quantities in the next subsections is due to the fact that each ω i will enter the MC‐TST equations as a multiplicative factor for the corresponding partition function of conformation i . We will return to this subject in the next subsections.…”

Section: Resultsmentioning

confidence: 99%

“…The lower barrier heights for the OH attack on

{HG}_{1}^{'}

‐10 provide an indication that such claim may be true, but additional factors must be taken into account when performing a complete kinetics study of these reactions through MC‐TST. Although this work does not concern particular details behind MC‐TST, visualizing the forward rate constant will help the reader understand how those factors interplay. We will adapt Equation 17 of Ref.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, for growing qp pairs, a huge amount of optimization procedures will be required in order to incorporate the multiple conformeric geometries of reactants and transition state structures into the kinetic calculations. Such rate constants can be obtained, for example, via multiconformer transition state theory (MC‐TST) . Acknowledging the large number of reactants and transition state structures that are needed for such a thorough investigation, the question then becomes: what will be the best cost‐effective electronic structure methodology yielding the necessary data to feed the MC‐TST equations?…”

Section: Introductionmentioning

confidence: 99%

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Assessment of model chemistries for hydrofluoropolyethers: A DFT/M08‐HX benchmark study

Viegas

2017

Int J of Quantum Chemistry

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In this work, we report the first detailed theoretical comparative conformational investigation between two different classes of hydrofluoropolyethers: dihydro-and dimethoxyfluoropolyethers.The main objective was to determine a cost-effective computational methodology that could accurately reproduce the energetic rankings and thermal weight factors of the simplest examples of those two classes calculated with M08-HX/triple-f//M08-HX/double-f benchmark model chemistries. Between the tested methodologies, M08-HX/aug-pcseg-2//M08-HX/pcseg-1 was found to be the most appropriate, exhibiting a good accuracy and considerable reduction in computational cost with respect to the benchmark, being more than three times faster than M08-HX/aug-pcseg-2//M08-HX/aug-pcseg-1. This cost-effective approach will be essential in future work when studying larger hydrofluoropolyethers, where the computational complexity associated with increasing number of conformers will require such approximations. K E Y W O R D S atmospheric chemistry, conformational sampling, density functional theory, hydrofluoropolyethers, model chemistry Int J Quantum Chem. 2017;117:e25381.

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“…All quantum chemical calculations were performed using the Gaussian-09 program suite (Frisch et al, 2010). The high-pressure rate coefficients for each of the elementary processes was then calculated using multi-conformer canonical transition state theory, MC-CTST (Vereecken and Peeters, 2003;Zheng and Truhlar, 2013) based on a rigid rotor harmonic oscillator paradigm, an exhaustive search of the reactants and TS conformers, and asymmetric Eckart tunnelling and WKB zerocurvature (ZCT) tunnelling. For the 1,4-and 1,6-H-shift in HMVKAO 2 , a large difference between Eckart and ZCT tunnelling was found; the geometric average is reported here (see Supplement).…”

Section: Quantum-chemical Calculationsmentioning

confidence: 99%

Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR

Fuchs¹,

Albrecht²,

Acir

et al. 2018

Atmos. Chem. Phys.

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Abstract. The photooxidation of methyl vinyl ketone (MVK) was investigated in the atmospheric simulation chamber SAPHIR for conditions at which organic peroxy radicals (RO 2 ) mainly reacted with NO ("high NO" case) and for conditions at which other reaction channels could compete ("low NO" case). Measurements of trace gas concentrations were compared to calculated concentration time series applying the Master Chemical Mechanism (MCM version 3.3.1). Product yields of methylglyoxal and glycolaldehyde were determined from measurements. For the high NO case, the methylglyoxal yield was (19 ± 3) % and the glycolaldehyde yield was (65 ± 14) %, consistent with recent literature studies. For the low NO case, the methylglyoxal yield reduced to (5 ± 2) % because other RO 2 reaction channels that do not form methylglyoxal became important. Consistent with literature data, the glycolaldehyde yield of (37 ± 9) % determined in the experiment was not reduced as much as implemented in the MCM, suggesting additional reaction channels producing glycolaldehyde. At the same time, direct quantification of OH radicals in the experiments shows the need for an enhanced OH radical production at low NO conditions similar to previous studies investigating the oxidation of the parent VOC isoprene and methacrolein, the second major oxidation product of isoprene. For MVK the model-measurement discrepancy was up to a factor of 2. Product yields and OH observations were consistent with assumptions of additional RO 2 plus HO 2 reaction channels as proposed in literature for the major RO 2 species formed from the reaction of MVK with OH. However, this study shows that also HO 2 radical concentrations are underestimated by the model, suggesting that additional OH is not directly produced from RO 2 radical reactions, but indirectly via increased HO 2 . Quantum chemical calculations show that HO 2 could be produced from a fast 1,4-H shift of the second most important MVK derived RO 2 species (reaction rate constant 0.003 s −1 ). However, additional HO 2 from this reaction was not sufficiently large to bring modelled HO 2 radical concentrations into agreement with measurements due to the small yield of this RO 2 species. An additional reaction channel of the major RO 2 species with a reaction rate constant of (0.006 ± 0.004) s −1 would be required that produces concurrently HO 2 radicals and glycolaldehyde to achieve modelmeasurement agreement. A unimolecular reaction similar to the 1,5-H shift reaction that was proposed in literature for RO 2 radicals from MVK would not explain product yields for conditions of experiments in this study. A set of H-migration reactions for the main RO 2 radicals were investigated by quantum chemical and theoretical kinetic methodologies, but did not reveal a contributing route to HO 2 radicals or glycolaldehyde.

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The 1,5-H-shift in 1-butoxy: A case study in the rigorous implementation of transition state theory for a multirotamer system

Cited by 124 publications

References 39 publications

Atmospheric autoxidation is increasingly important in urban and suburban North America

Atmospheric autoxidation is increasingly important in urban and suburban North America

Assessment of model chemistries for hydrofluoropolyethers: A DFT/M08‐HX benchmark study

Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR

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