Ab initio study of hydrogen abstraction reactions on toluene and tetralin

Beste, Ariana; Buchanan, A. C.; Britt, Phillip F.; Hathorn, Bryan C.; Harrison, Robert J.

doi:10.1016/j.theochem.2007.11.015

Cited by 9 publications

(8 citation statements)

References 36 publications

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“…As previously noted, M06-2X has been shown to provide reliable estimates of energy barriers. The significantly lower energy barrier from B3LYP is consistent with previous studies that noted its underestimation of energy barriers. ,,,− The MP2 barrier is the highest, which is consistent with other studies that noted a tendency for MP2 to overestimate energy barriers. ,, …”

Section: Resultssupporting

confidence: 90%

“…35,38,66,68−70 The MP2 barrier is the highest, which is consistent with other studies that noted a tendency for MP2 to overestimate energy barriers. 66,69,71 For cellulose, a midchain initial concerted glycosidic cleavage yields two polymeric fragments: a cellulose-like polymer with a terminal levoglucosan-like end and a shorter cellulose chain. Thus, the initiation step can be followed by depropagation steps in which a molecule of levoglucosan is released from the chain end for each subsequent scission of a glycosidic bond.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Unraveling the Reactions that Unravel Cellulose

2012

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For over 90 years, researchers have postulated mechanisms for the cleavage of cellulose's glycosidic bonds and resulting formation of levoglucosan without reaching consensus. These reactions are key primary reactions in thermal processes for the production of carbon-neutral, renewable transportation fuels. Previous literature reports have proposed a variety of mainly heterolytic and homolytic mechanisms, but there has been insufficient evidence to settle the debate. Using density functional theory (DFT) methods and implicit solvent, we compared the likelihood of forming either radical or ionic intermediates. We discovered a concerted reaction mechanism that is more favorable than previously proposed mechanisms and is in better alignment with experimental findings. This new understanding of the mechanism of cellulose thermal decomposition opens the door to accurate process modeling and educated catalyst design, which are vital steps toward producing more cost-efficient renewable energy.

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Section: Resultssupporting

confidence: 90%

Section: ■ Results and Discussionmentioning

confidence: 99%

Unraveling the Reactions that Unravel Cellulose

2012

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“…In 2007, radical chain reactions in lignin pyrolysis were first probed by comparing the product formation pathways that involved the hydrogen abstraction at the α and β positions of the β−O−4 linkage (α and β paths). 100 Later, the same team carried out systematic QC modeling studies on lignin pyrolysis, including the hydrogen abstraction reactions of toluene and tetralin, 101 the hydrogen abstraction mechanism of oxygen-substituted lignin dimers, 102 the BDEs of typical linkages in substituted lignin dimers, 103,104 the substituent effects on hydrogen abstraction, 105 the phenyl-shift reactions (C−O rearrangement 106 and C−C rearrangement 107 ), the complete radical chain reactions, 108 the α-hydroxy effects for hydrogen abstraction, 109 the concerted reactions in lignin pyrolysis, 110 and other related topics.…”

Section: Qc Modeling and Its Application Tomentioning

confidence: 99%

Recent Progress in Quantum Chemistry Modeling on the Pyrolysis Mechanisms of Lignocellulosic Biomass

et al. 2020

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Pyrolysis of lignocellulose biomass to produce various fuels and chemicals has gained increasing interest in recent decades. An in-depth understanding of the biomass pyrolysis reaction mechanisms is essential for the advancement of pyrolysis techniques. Quantum chemistry (QC) modeling is a powerful approach for the pyrolysis mechanism investigation at the atomic/molecular level. Despite a short history of only about 2 decades, its application to the biomass pyrolysis mechanism exploration has been well-developed, along with the fast advances of supercomputer and computational codes in the new century. This review addresses the recent progress on the pyrolysis mechanism of the three basic biomass components (cellulose, hemicellulose, and lignin) by QC modeling. On the basis of the QC modeling results reported in the literature, the current review critically summarizes the key developments about the pyrolysis chemistry of biomass by focusing on their microscopic elementary reactions, the formation routes of typical products, bimolecular interactions within or between biomass components, and catalytic effects of various catalysts. Notably, there are great gaps between the theoretical models employed in QC modeling and the natural biomass substance in the pyrolysis process. Therefore, a brief analysis of the challenges and future research perspectives is provided for the biomass pyrolysis mechanism research.

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“…We use density functional theory (B3LYP) to accommodate the medium-size molecules. The transition states located for the pyrolysis of PPE 3 and for similar reactions 14 showed spurious imaginary frequencies that are caused by a flat potential energy surface in combination with the breakdown of the harmonic approximation. For such frequencies the harmonic partition function is not defined.…”

Section: Introductionmentioning

confidence: 99%

Computational Prediction of α/β Selectivities in the Pyrolysis of Oxygen-Substituted Phenethyl Phenyl Ethers

2008

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Phenethyl phenyl ether (PPE; PhCH 2CH 2OPh) is the simplest model for the most common beta-O-4 linkage in lignin. Previously, we developed a computational scheme to calculate the alpha/beta product selectivity in the pyrolysis of PPE by systematically exploiting error cancellation in the computation of relative rate constants. The alpha/beta selectivity is defined as the selectivity between the competitive hydrogen abstraction reaction paths on the alpha- and beta-carbons of PPE. We use density functional theory and employ transition state theory where we include diagonal anharmonic correction in the vibrational partition functions for low frequency modes for which a semiclassical expression is used. In this work we investigate the effect of oxygen substituents (hydroxy, methoxy) in the para position on the phenethyl ring of PPE on the alpha/beta selectivities. The total alpha/beta selectivity increases when substituents are introduced and is larger for the methoxy than the hydroxy substituent. The strongest effect of the substituents is observed for the alpha-pathway of the hydrogen abstraction by the phenoxyl chain carrying radical for which the rate increases. For the beta pathway and the abstraction by the R-benzyl radical (R = OH,OCH 3) the rate decreases with the introduction of the substituents. These findings are compared with results from recent experimental studies.

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Ab initio study of hydrogen abstraction reactions on toluene and tetralin

Cited by 9 publications

References 36 publications

Unraveling the Reactions that Unravel Cellulose

Unraveling the Reactions that Unravel Cellulose

Recent Progress in Quantum Chemistry Modeling on the Pyrolysis Mechanisms of Lignocellulosic Biomass

Computational Prediction of α/β Selectivities in the Pyrolysis of Oxygen-Substituted Phenethyl Phenyl Ethers

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