Topic
Transition state
About: Transition state is a research topic. Over the lifetime, 4978 publications have been published within this topic receiving 117965 citations. The topic is also known as: transition state of elementary reaction.
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TL;DR: URVA can show the mechanism of a reaction expressed in terms of reaction phases, revealing the sequence of chemical processes in the reaction complex and making it possible to determine those electronic factors that control the mechanism and energetics of the reaction.
Abstract: Computational approaches to understanding chemical reaction mechanisms generally begin by establishing the relative energies of the starting materials, transition state, and products, that is, the stationary points on the potential energy surface of the reaction complex. Examining the intervening species via the intrinsic reaction coordinate (IRC) offers further insight into the fate of the reactants by delineating, step-by-step, the energetics involved along the reaction path between the stationary states. For a detailed analysis of the mechanism and dynamics of a chemical reaction, the reaction path Hamiltonian (RPH) and the united reaction valley approach (URVA) are an efficient combination. The chemical conversion of the reaction complex is reflected by the changes in the reaction path direction t(s) and reaction path curvature k(s), both expressed as a function of the path length s. This information can be used to partition the reaction path, and by this the reaction mechanism, of a chemical reaction...
145 citations
TL;DR: Kinetic simulation results for a high temperature pyrolysis environment show that MB radicals are mainly produced through hydrogen abstraction reactions by H atoms, and the C(O)OCH(3) = CO + CH( 3)O reaction is found to be the main source of CO formation.
Abstract: In this paper, we report a detailed analysis of the breakdown kinetic mechanism for methyl butanoate (MB) using theoretical approaches. Electronic structures and structure-related molecular properties of reactants, intermediates, products, and transition states were explored at the BH&HLYP/cc-pVTZ level of theory. Rate constants for the unimolecular and bimolecular reactions in the temperature range of 300−2500 K were calculated using Rice−Ramsperger−Kassel−Marcus and transition state theories, respectively. Thirteen pathways were identified leading to the formation of small compounds such as CH3, C2H3, CO, CO2, and H2CO. For the initial formation of MB radicals, H, CH3, and OH were considered as reactive radicals participating in hydrogen abstraction reactions. Kinetic simulation results for a high temperature pyrolysis environment show that MB radicals are mainly produced through hydrogen abstraction reactions by H atoms. In addition, the C(O)OCH3 = CO + CH3O reaction is found to be the main source of C...
145 citations
TL;DR: In this paper, a simplified theoretical model was constructed in terms of the intrinsic reaction coordinate (IRC) and normal coordinates perpendicular to it for the four-centered elimination reaction CH3CH2F→HF+CH2CH2.
Abstract: The mechanism of energy disposal along the reaction pathway was discussed in relation to the characteristic features of potential energy surface. A simplified theoretical model was constructed in terms of the intrinsic reaction coordinate (IRC) and normal coordinates perpendicular to it. Ab initio MO calculations with the split‐valence basis set were carried out for the four‐centered elimination reaction CH3CH2F→HF+CH2CH2. The energy gradient method was used to optimize the stationary points on the potential surface and to trace IRC as well as to calculate the force constants. The origin of vibrational enhancement of HF in the reaction product was interpreted as the result of interchange of the main components of IRC in a local region where the IRC curvature is large.
143 citations
TL;DR: In this paper, the authors investigated several catalytic reactions on some transition metal surfaces, using density functional theory, and determined all the reaction barriers related to the potential energy surface of reactants on the surface, the total chemisorption energy of reactant, and the metal d orbital occupancy and the reactant valency.
Abstract: A catalyst preparation by design is one of the ultimate goals in chemistry. The first step towards this goal is to understand the origin of reaction barriers. In this study, we have investigated several catalytic reactions on some transition metal surfaces, using density functional theory. All the reaction barriers have been determined. By detailed analyses we obtain some insight into the reaction barrier. Each barrier is related to (i) the potential energy surface of reactants on the surface, (ii) the total chemisorption energy of reactants, and (iii) the metal d orbital occupancy and the reactant valency.
142 citations
TL;DR: In this paper, two different kinds of semiclassical approximations are used to evaluate a previously obtained quantum mechanical transition state theory rate expression for the collinear H+H2 reaction.
Abstract: Two different kinds of semiclassical approximations are used to evaluate a previously obtained quantum mechanical transition state theory rate expression. No assumptions, however, such as separability of the Hamiltonian, vibrationally adiabatic motion along a reaction coordinate, etc., are incorporated. Application is made to the collinear H+H2 reaction, and agreement with accurate quantum scattering calculations is found to be reasonably good. The results indicate that transition state theory—provided no assumptions of separability are included—is probably as accurate quantum mechanically as it has been found to be classically for describing the threshold of chemical reactions with an activation barrier.
142 citations