An integrated protocol to study hydrogen abstraction reactions by atomic hydrogen in flexible molecules: application to butanol isomers

Ferro-Costas, David; Cordeiro, M. Natália D. S.; Fernández‐Ramos, Antonio

doi:10.1039/d1cp03928h

Cited by 7 publications

(4 citation statements)

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“…For most species, the MS-T(CD) factors first increase with temperature until reaching the maximum value, and then decrease monotonically, while for others the MS-T(CD) factors keep decreasing over the whole temperature range. This phenomenon should be attributed to the fact that the density of states of the hindered rotor partition function decreases as temperature rises, whereas it remains constant for the harmonic oscillator . In general, the MS-T(CD) factor spreads over ranges of 0.53–7.60, 0.79–6.63 and 0.49–5.01 for D12MCH+OH, D13MCH+OH and D14MCH+OH systems, respectively.…”

Section: Results and Discussionmentioning

confidence: 98%

“…For D13MCH+OH, R5e with the GTS located in the range of −0.36 − −0.26 a 0 shows the strongest variational effect and has the CVT recrossing transmission coefficient being 0.13 at 200 K and 0.68 at 2000 K. For D14MCH+OH, R2 with the GTS located from −0.43 to −0.11 a 0 and R1 with the GTS located from −0.34 to −0.31 show the weakest and the strongest variational effect, respectively as temperature changes from 200 to 2000 K. Generally, this pronounced variational effect is attributed to the vibrational normal mode corresponding to the approach of donor and acceptor atoms, which changes rapidly along the reaction path as the C−H bonds break and the new O−H bonds form. 75,76 In summary, the CVT recrossing transmission coefficients lie in the range of 0.12−0.95 at 200−2000 K, and different abstraction sites have different temperature-dependent variational features. Therefore, the kinetics treatment using the variational transition state theory is indispensable for our studied abstraction reactions.…”

Section: Transmission Coefficientsmentioning

confidence: 96%

“…This phenomenon should be attributed to the fact that the density of states of the hindered rotor partition function decreases as temperature rises, whereas it remains constant for the harmonic oscillator. 75 In general, the MS-T(CD) factor spreads over ranges of 0. than reactants, the torsional anharmonicity leads to the decrease of rate constants with a maximum deviation of more than 5 times. In other words, the contributions of all conformational structures may cause obvious overpredictions of rate constants if the further coupled torsional potential is not considered.…”

Section: Multistructural Torsional Anharmonicitymentioning

confidence: 99%

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Comprehensive Multipath Variational Kinetics Study on Hydrogen Abstraction Reactions from Three Typical Dimethylcyclohexane Isomers by Hydroxyl Radicals: from the Electronic Structure to Model Applications

Yang,

Wang

2024

J. Phys. Chem. A

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Cycloalkanes serve as an important class of chemical components in both fossil and alternative transportation fuels and have attracted considerable attention from the combustion community. Hydrogen abstractions from cycloalkanes by hydroxyl radicals initiate the fuel decomposition process and trigger off the subsequent chain reactions and thus play an important role in both combustion and atmospheric chemistry. The target of this study is to fill the vacancy in kinetics data toward the H-abstraction reactions by hydroxyl radical from three typical dimethylcyclohexane isomers through first-principles and direct dynamics. The rate constants involving 18 elementary reactions in total were accurately determined by the multipath canonical variational transition state theory with the multidimensional small-curvature correction for tunneling (MP-CVT/SCT), over a broad temperature range of 200−2000 K. The significant roles of multistructural torsional anharmonicity and recrossing effects were stressed per abstraction site, while the quantum tunneling effect was found to be slight at temperatures of interest in combustion. The discrepancies observed among different reaction systems at a similar abstraction site highlight the fuel molecular effects on site-specific rate constants. The comparison results of total rate constants given by different dynamics approaches prove the importance of considering the torsional anharmonicity, recrossing, and tunneling effects, and the robust feature of the simplified MS-CVT/SCT. The calculated total constants for dimethylcyclohexane isomers by OH are consistent with those measured for methylcyclohexane and 1,4-dimethylcyclohexane at low temperatures. The branching ratio analysis confirms the predominant role of the tertiary abstraction at low-to-intermediate temperatures and its growing competition with distinct secondary abstractions as temperature increases. The calculated rate constants were eventually fitted into the analytical expressions and incorporated into the kinetic models to learn about the influences on modeling performance.

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Section: Results and Discussionmentioning

confidence: 98%

Section: Transmission Coefficientsmentioning

confidence: 96%

Section: Multistructural Torsional Anharmonicitymentioning

confidence: 99%

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Comprehensive Multipath Variational Kinetics Study on Hydrogen Abstraction Reactions from Three Typical Dimethylcyclohexane Isomers by Hydroxyl Radicals: from the Electronic Structure to Model Applications

Yang,

Wang

2024

J. Phys. Chem. A

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“…The computational details presented in this section for calculating the thermal rate constants to (R δ )−(R OH ) follow the protocol to study hydrogen abstraction reactions by atomic hydrogen in flexible molecules, recently developed by Ferro-Costas et al 22 As a first step, employing an inexpensive level of theory (HF/3-21G), 23 a systematic conformational search, based on chemical knowledge, was performed for the stationary points generated by the reactions (R δ )−(R OH ). The torsions used in this scanning were depicted in Figure 1.…”

Section: ■ Computational Detailsmentioning

confidence: 99%

Prenol as a Next-Generation Biofuel or Additive: A Comprehension of the Hydrogen Abstraction Reactions by a H Atom

2022

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Thermal rate coefficients for the hydrogen abstraction reactions of prenol (3-methyl-2-butenol) by a hydrogen atom were calculated with the multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT). The conformational search was performed with a dual-level approach, and the multistructural torsional anharmonicity effects were corrected through the rovibrational partition function calculated with the multistructural method based on a coupled torsional potential (MS-T(C)). This methodology allows us to estimate the thermal rate constants in the temperature range of 200–2500 K and fit them into two analytical expressions. Differences between the number of conformations on the torsional potential energy surfaces for prenol and the transition state decrease the thermal rate constants for the H-abstraction at the α carbon. An opposite behavior was detected for the abstractions on the δ site. The product branching ratios were calculated using single-structure and multipath approaches. The product distributions from the former are shown to be inadequate for studying the mechanism under combustion conditions. The values estimated from MP-CVT/SCT rate coefficients indicated that the radicals from (R α) and (R δ)/(R δ′) are formed in considerable amounts. These species are fundamental in comprehending the inhibition and promotion of the autoignition phenomena.

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New computational tools for chemical kinetics: the Cathedral Package

Ferro-Costas,

Fernández-Ramos

2023

Theor Chem Acc

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The advent of recent technological developments in software engineering has enabled the exploration of reaction mechanisms inside intricate reaction networks, thereby propelling the beginning of a new era in ab initio kinetics. While it is feasible to consider a substantial number of reactions, determining their rate constants with precision remains an arduous task, even for gas-phase processes. The difficulties are attributed not only to the inherent limitations in the calculation methodology but also to the manual labor and extensive chemical dynamics required, rendering these calculations inaccessible to the general public. As such, there is a pressing need for the development of automated codes and user-friendly interfaces to address this limitation. The present work focuses on the introduction of the Cathedral package, a unified computational code comprising the , , and programs. This package serves to bridge the gap between theoretical studies in chemical kinetics and non-specialist users, making it more accessible and user-friendly.

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An integrated protocol to study hydrogen abstraction reactions by atomic hydrogen in flexible molecules: application to butanol isomers

Abstract: This work presents a protocol designed to study hydrogen abstraction reactions by atomic hydrogen in molecules with multiple conformations. The protocol starts with the search and location of the conformers...

Cited by 7 publications

References 77 publications

Comprehensive Multipath Variational Kinetics Study on Hydrogen Abstraction Reactions from Three Typical Dimethylcyclohexane Isomers by Hydroxyl Radicals: from the Electronic Structure to Model Applications

Comprehensive Multipath Variational Kinetics Study on Hydrogen Abstraction Reactions from Three Typical Dimethylcyclohexane Isomers by Hydroxyl Radicals: from the Electronic Structure to Model Applications

Prenol as a Next-Generation Biofuel or Additive: A Comprehension of the Hydrogen Abstraction Reactions by a H Atom

New computational tools for chemical kinetics: the Cathedral Package

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