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Lam K Huynh - One of the best experts on this subject based on the ideXlab platform.
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performance of first principles based Reaction Class transition state theory
Journal of Physical Chemistry B, 2016Co-Authors: Artur Ratkiewicz, Lam K Huynh, Thanh N. TruongAbstract:Performance of the Reaction Class Transition State Theory (RC-TST) for prediction of rates constants of elementary Reactions is examined using data from its previous applications to a number of different Reaction Classes. The RC-TST theory is taking advantage of the common structure denominator of all Reactions in a given family combined with structure activity relationships to provide a rigorous theoretical framework to obtain rate expression of any Reaction within a Reaction Class in a simple and cost-effective manner. This opens the possibility for integrating this methodology with an automated mechanism generator for “on-the-fly” generation of accurate kinetic models of complex reacting systems.
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high pressure rate rules for alkyl o2 Reactions 2 the isomerization cyclic ether formation and β scission Reactions of hydroperoxy alkyl radicals
Journal of Physical Chemistry A, 2012Co-Authors: Stephanie M Villano, Lam K Huynh, Hansheinrich Carstensen, Anthony M DeanAbstract:The unimolecular Reactions of hydroperoxy alkyl radicals (QOOH) play a central role in the low-temperature oxidation of hydrocarbons as they compete with the addition of a second O2 molecule, which is known to provide chain-branching. In this work we present high-pressure rate estimation rules for the most important unimolecular Reactions of the β-, γ-, and δ-QOOH radicals: isomerization to RO2, cyclic ether formation, and selected β-scission Reactions. These rate rules are derived from high-pressure rate constants for a series of Reactions of a given Reaction Class. The individual rate expressions are determined from CBS-QB3 electronic structure calculations combined with canonical transition state theory calculations. Next we use the rate rules, along with previously published rate estimation rules for the Reactions of alkyl peroxy radicals (RO2), to investigate the potential impact of falloff effects in combustion/ignition kinetic modeling. Pressure effects are examined for the Reaction of n-butyl radi...
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high pressure rate rules for alkyl o2 Reactions 1 the dissociation concerted elimination and isomerization channels of the alkyl peroxy radical
Journal of Physical Chemistry A, 2011Co-Authors: Stephanie M Villano, Lam K Huynh, Hansheinrich Carstensen, Anthony M DeanAbstract:The Reactions of alkyl peroxy radicals (RO2) play a central role in the low-temperature oxidation of hydrocarbons. In this work, we present high-pressure rate estimation rules for the dissociation, concerted elimination, and isomerization Reactions of RO2. These rate rules are derived from a systematic investigation of sets of Reactions within a given Reaction Class using electronic structure calculations performed at the CBS-QB3 level of theory. The rate constants for the dissociation Reactions are obtained from calculated equilibrium constants and a literature review of experimental rate constants for the reverse association Reactions. For the concerted elimination and isomerization channels, rate constants are calculated using canonical transition state theory. To determine if the high-pressure rate expressions from this work can directly be used in ignition models, we use the QRRK/MSC method to calculate apparent pressure and temperature dependent rate constants for representative Reactions of small, ...
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kinetics of the hydrogen abstraction ch3 alkane ch4 alkyl Reaction Class an application of the Reaction Class transition state theory
Journal of Physical Chemistry A, 2005Co-Authors: Lam K Huynh, Artur Ratkiewicz, Thanh N. TruongAbstract:This paper presents an application of the Reaction Class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction Reactions of the type OH + alkane --> HOH + alkyl. We have derived all parameters for the RC-TST method for this Reaction Class from rate constants of 19 representative Reactions, coupling with linear energy relationships (LERs), so that rate constants for any Reaction in this Class can be predicted from its Reaction energy calculated at either the AM1 semiempirical or BH&HLYP/cc-pVDZ level of theory. The RC-TST/LER thermal rate constants for selected Reactions are in good agreement with those available in the literature. Detailed analyses of the results show that the RC-TST/LER method is an efficient method for accurately estimating rate constants for a large number of Reactions in this Class. Analysis of the LERs leads to the discovery of the beta-carbon radical stabilization effect that stabilizes the transition state of any Reaction in this Class that yields products having one or more beta-carbons, and thus leads to the lower barrier for such a Reaction.
Thijs Stuyver - One of the best experts on this subject based on the ideXlab platform.
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electrophilic aromatic substitution Reactions mechanistic landscape electrostatic and electric field control of Reaction rates and mechanistic crossovers
Journal of the American Chemical Society, 2019Co-Authors: Thijs Stuyver, David Danovich, Frank De Proft, Sason ShaikAbstract:This study investigates the rich mechanistic landscape of the iconic electrophilic aromatic substitution (EAS) Reaction Class, in the gas phase, in solvents, and under stimulation by oriented external electric fields. The study uses DFT calculations, complemented by a qualitative valence bond (VB) perspective. We construct a comprehensive and unifying framework that elucidates the many surprising mechanistic features, uncovered in recent years, of this Class of Reactions. For example, one of the puzzling issues which have attracted significant interest recently is the finding of a variety of concerted mechanisms that do not involve the formation of σ-complex intermediates, in apparent contradiction to the generally accepted textbook mechanism. Our VB modeling elucidates the existence of both the concerted and stepwise mechanisms and uncovers the root causes and necessary conditions for the appearance of these intermediates. Furthermore, our VB analysis offers insight into the potential applications of ext...
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electrophilic aromatic substitution Reactions mechanistic landscape electrostatic and electric field control of Reaction rates and mechanistic crossovers
Journal of the American Chemical Society, 2019Co-Authors: Thijs Stuyver, David Danovich, Frank De Proft, Sason ShaikAbstract:This study investigates the rich mechanistic landscape of the iconic electrophilic aromatic substitution (EAS) Reaction Class, in the gas phase, in solvents, and under stimulation by oriented external electric fields. The study uses DFT calculations, complemented by a qualitative valence bond (VB) perspective. We construct a comprehensive and unifying framework that elucidates the many surprising mechanistic features, uncovered in recent years, of this Class of Reactions. For example, one of the puzzling issues which have attracted significant interest recently is the finding of a variety of concerted mechanisms that do not involve the formation of σ-complex intermediates, in apparent contradiction to the generally accepted textbook mechanism. Our VB modeling elucidates the existence of both the concerted and stepwise mechanisms and uncovers the root causes and necessary conditions for the appearance of these intermediates. Furthermore, our VB analysis offers insight into the potential applications of external electric fields as smart, green, and selective catalysts, which can control at will Reaction rates, as well as mechanistic crossovers, for this Class of Reactions. Finally, we highlight how understanding of the electric fields effect on the EAS Reaction could lead to the formulation of guiding principles for the design of improved heterogeneous catalysts. Overall, our analysis underscores the powerful synergy offered by combining molecular orbital and VB theory to tackle interesting and challenging mechanistic questions in chemistry.
Thanh N. Truong - One of the best experts on this subject based on the ideXlab platform.
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performance of first principles based Reaction Class transition state theory
Journal of Physical Chemistry B, 2016Co-Authors: Artur Ratkiewicz, Lam K Huynh, Thanh N. TruongAbstract:Performance of the Reaction Class Transition State Theory (RC-TST) for prediction of rates constants of elementary Reactions is examined using data from its previous applications to a number of different Reaction Classes. The RC-TST theory is taking advantage of the common structure denominator of all Reactions in a given family combined with structure activity relationships to provide a rigorous theoretical framework to obtain rate expression of any Reaction within a Reaction Class in a simple and cost-effective manner. This opens the possibility for integrating this methodology with an automated mechanism generator for “on-the-fly” generation of accurate kinetic models of complex reacting systems.
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kinetics of the hydrogen abstraction ch3 alkane ch4 alkyl Reaction Class an application of the Reaction Class transition state theory
Journal of Physical Chemistry A, 2005Co-Authors: Lam K Huynh, Artur Ratkiewicz, Thanh N. TruongAbstract:This paper presents an application of the Reaction Class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction Reactions of the type OH + alkane --> HOH + alkyl. We have derived all parameters for the RC-TST method for this Reaction Class from rate constants of 19 representative Reactions, coupling with linear energy relationships (LERs), so that rate constants for any Reaction in this Class can be predicted from its Reaction energy calculated at either the AM1 semiempirical or BH&HLYP/cc-pVDZ level of theory. The RC-TST/LER thermal rate constants for selected Reactions are in good agreement with those available in the literature. Detailed analyses of the results show that the RC-TST/LER method is an efficient method for accurately estimating rate constants for a large number of Reactions in this Class. Analysis of the LERs leads to the discovery of the beta-carbon radical stabilization effect that stabilizes the transition state of any Reaction in this Class that yields products having one or more beta-carbons, and thus leads to the lower barrier for such a Reaction.
Chongwen Zhou - One of the best experts on this subject based on the ideXlab platform.
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an experimental and chemical kinetic modeling study of 1 3 butadiene combustion ignition delay time and laminar flame speed measurements
Combustion and Flame, 2018Co-Authors: Chongwen Zhou, Ultan Burke, Colin Banyon, Kieran P Somers, Shuiting Ding, Saadat Khan, Joshua W Hargis, Travis Sikes, Olivier MathieuAbstract:Abstract Ignition delay times for 1,3-butadiene oxidation were measured in five different shock tubes and in a rapid compression machine (RCM) at thermodynamic conditions relevant to practical combustors. The ignition delay times were measured at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’ at pressures of 10, 20 and 40 atm in both the shock tubes and in the RCM. Additional measurements were made at equivalence ratios of 0.3, 0.5, 1.0 and 2.0 in argon, at pressures of 1, 2 and 4 atm in a number of different shock tubes. Laminar flame speeds were measured at unburnt temperatures of 295 K, 359 K and 399 K at atmospheric pressure in the equivalence ratio range of 0.6–1.7, and at a pressure of 5 atm at equivalence ratios in the range 0.6–1.4. These experimental data were then used as validation targets for a newly developed detailed chemical kinetic mechanism for 1,3-butadiene oxidation. A detailed chemical kinetic mechanism (AramcoMech 3.0) has been developed to describe the combustion of 1,3-butadiene and is validated by a comparison of simulation results to the new experimental measurements. Important Reaction Classes highlighted via sensitivity analyses at different temperatures include: (a) ȮH radical addition to the double bonds on 1,3-butadiene and their subsequent Reactions. The branching ratio for addition to the terminal and central double bonds is important in determining the reactivity at low-temperatures. The alcohol-alkene radical adducts that are subsequently formed can either react with HȮ2 radicals in the case of the resonantly stabilized radicals or O2 for other radicals. (b) HȮ2 radical addition to the double bonds in 1,3-butadiene and their subsequent Reactions. This Reaction Class is very important in determining the fuel reactivity at low and intermediate temperatures (600–900 K). Four possible addition Reactions have been considered. (c) 3O atom addition to the double bonds in 1,3-butadiene is very important in determining fuel reactivity at intermediate to high temperatures (> 800 K). In this Reaction Class, the formation of two stable molecules, namely CH2O + allene, inhibits reactivity whereas the formation of two radicals, namely Ċ2H3 and ĊH2CHO, promotes reactivity. (d) Ḣ atom addition to the double bonds in 1,3-butadiene is very important in the prediction of laminar flame speeds. The formation of ethylene and a vinyl radical promotes reactivity and it is competitive with H-atom abstraction by Ḣ atoms from 1,3-butadiene to form the resonantly stabilized Ċ4H5-i radical and H2 which inhibits reactivity. Ab initio chemical kinetics calculations were carried out to determine the thermochemistry properties and rate constants for some of the important species and Reactions involved in the model development. The present model is a decent first model that captures most of the high-temperature IDTs and flame speeds quite well, but there is room for considerable improvement especially for the lower temperature chemistry before a robust model is developed.
Anthony M Dean - One of the best experts on this subject based on the ideXlab platform.
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high pressure rate rules for alkyl o2 Reactions 2 the isomerization cyclic ether formation and β scission Reactions of hydroperoxy alkyl radicals
Journal of Physical Chemistry A, 2012Co-Authors: Stephanie M Villano, Lam K Huynh, Hansheinrich Carstensen, Anthony M DeanAbstract:The unimolecular Reactions of hydroperoxy alkyl radicals (QOOH) play a central role in the low-temperature oxidation of hydrocarbons as they compete with the addition of a second O2 molecule, which is known to provide chain-branching. In this work we present high-pressure rate estimation rules for the most important unimolecular Reactions of the β-, γ-, and δ-QOOH radicals: isomerization to RO2, cyclic ether formation, and selected β-scission Reactions. These rate rules are derived from high-pressure rate constants for a series of Reactions of a given Reaction Class. The individual rate expressions are determined from CBS-QB3 electronic structure calculations combined with canonical transition state theory calculations. Next we use the rate rules, along with previously published rate estimation rules for the Reactions of alkyl peroxy radicals (RO2), to investigate the potential impact of falloff effects in combustion/ignition kinetic modeling. Pressure effects are examined for the Reaction of n-butyl radi...
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high pressure rate rules for alkyl o2 Reactions 1 the dissociation concerted elimination and isomerization channels of the alkyl peroxy radical
Journal of Physical Chemistry A, 2011Co-Authors: Stephanie M Villano, Lam K Huynh, Hansheinrich Carstensen, Anthony M DeanAbstract:The Reactions of alkyl peroxy radicals (RO2) play a central role in the low-temperature oxidation of hydrocarbons. In this work, we present high-pressure rate estimation rules for the dissociation, concerted elimination, and isomerization Reactions of RO2. These rate rules are derived from a systematic investigation of sets of Reactions within a given Reaction Class using electronic structure calculations performed at the CBS-QB3 level of theory. The rate constants for the dissociation Reactions are obtained from calculated equilibrium constants and a literature review of experimental rate constants for the reverse association Reactions. For the concerted elimination and isomerization channels, rate constants are calculated using canonical transition state theory. To determine if the high-pressure rate expressions from this work can directly be used in ignition models, we use the QRRK/MSC method to calculate apparent pressure and temperature dependent rate constants for representative Reactions of small, ...
