Ab initio study on the thermal decarboxylation of but-3-enoic acid and its derivatives

1994 ◽  
Vol 72 (5) ◽  
pp. 1338-1346 ◽  
Author(s):  
Youliang Wang ◽  
Raymond A. Poirier
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Ab Initio ◽  
Negative Charge ◽  
Enoic Acid ◽  
Electronic Charge ◽  
Theoretical Point ◽  
Cyclic Transition ◽  
Experimental Values ◽  
Thermal Decarboxylation

The mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives HXC=CYCH2COOH (X, Y=H, F, CH3, C2H5, and Cl) leading to carbon dioxide and olefins has been studied from the theoretical point of view by ab initio MO calculations. The transition states obtained by our ab initio calculations are completely consistent with the experimental data, and support the "synchronous" mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives via a "twisted chair" six-membered cyclic transition state. The effects of β- and γ-substituents on the activation energy (Ea) can be explained in terms of electronic charge distribution. β-Substitution decreases the activation energy, while γ-substitution increases it. Changes in the activation energy are related to changes in the charges at Cγ(C1) and Cβ(C2) as the substituents are varied. The activation energy decreases with an increase of negative charge at Cγ, while it increases with an increase of negative charge at Cβ. The best estimate of 156.8 kJ/mol for the activation energy with MP2/6-31G*//HF/3-21G(*) is in reasonable agreement with the available experimental values of 164 ± 7 kJ/mol and 160 kJ/mol for decarboxylation of but-3-enoic acid. The calculated primary kH/kD, 2.86, and [Formula: see text] 1.03, for the decarboxylation of but-3-enoic acid, are also in excellent agreement with the available experimental values of 2.7 and 1.035, respectively, supporting the transition state structure obtained.

Expanding the scope of the Newman–Kwart rearrangement — A computational assessment

2006 ◽  
Vol 84 (11) ◽  
pp. 1567-1574 ◽  
Author(s):  
Heiko Jacobsen ◽  
James P Donahue
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Structural Element ◽  
Cyclic Transition ◽  
Cyclic Transition State ◽  
Localized Orbital

The Newman–Kwart rearrangement (NKR) has been studied for a variety of thioncarbamates using density functional (B3LYP) and ab initio (MP2) methodologies. The results confirm and support the generally accepted mechanism that the NKR proceeds through a four-membered cyclic transition state. The presence of a π system connected via an oxygen linkage to a thiocarbonyl functionality is identified as a crucial structural element for the NKR. The calculations further suggest that the NKR might also be feasible for thioncarbamates derived from π system containing groups other than phenols such as ethenol, ethenediol, and butadienol. The NKR is compared with the Schönberg rearrangements of thioncarbonates.Key words: density functional calculations, localized orbital locator, oxygen–sulfur transposition, thiols.

On the structure of S42+ and its formation from 2S2+•Ab initio SCF and CASSCF studies

1994 ◽  
Vol 72 (2) ◽  
pp. 298-303 ◽  
Author(s):  
Mousumi Sannigrahi ◽  
Friedrich Grein
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Minimum Energy ◽  
Vibrational Frequencies ◽  
Square Planar ◽  
Experimental Values ◽  
Minimum Energy Paths

Ab initio studies up to the MP2/6-31G* level were performed on the geometry and energy of S42+. Eleven different structures were considered. In the RHF/6-31G* method, the square structure is the most stable, followed by the trans-planar C2h structure. S42+ (square) is 105.9 kcal/mol less stable than 2S22+. Minimum energy paths were calculated for the reaction 2S2+ → S42+, both in C2v and D2h symmetry. Using RHF/6-31G*, the transition state lies about 50 kcal/mol above the energy of square planar S42+. Using CASSCF or MP2 methods this energy can be significantly lowered (to about 33 kcal/mol in MP2/6-31G*). Calculated vibrational frequencies for the square structure are also given and compared with experimental values.

Concentration-Dependence of Self-Interstitial and Boron Diffusion in Silicon

2008 ◽  
Vol 1070 ◽  
Author(s):  
Wolfgang Windl
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Ab Initio Calculations ◽  
Fermi Level ◽  
Total Energy ◽  
Ab Initio ◽  
The Self ◽  
Recent Experimental Data ◽  
Boron Diffusion ◽  
Experimental Values

ABSTRACTIn this paper, we discuss the accuracy of ab-initio calculations for self-interstitial and boron dif-fusion in silicon in light of recent experimental data by de Salvador et al. and Bracht et al. Map-ping the experimental data onto the activation energy vs. Fermi level representation commonly used to display ab-initio results, we show that the experimental results are consistent with each other. While the theoretical LDA value for the boron activation energy as a function of the Fermi level agrees well with experiment, we find for the self-interstitial in line with other calculations an underestimation of the experimental values, despite using total-energy corrections.

Ab Initio Calculations for Hydrocarbons:  Enthalpy of Formation, Transition State Geometry, and Activation Energy for Radical Reactions

2003 ◽  
Vol 107 (43) ◽  
pp. 9147-9159 ◽  
Author(s):  
Mark Saeys ◽  
Marie-Françoise Reyniers ◽  
Guy B. Marin ◽  
Veronique Van Speybroeck ◽  
Michel Waroquier
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Enthalpy Of Formation ◽  
Radical Reactions ◽  
Transition State Geometry

Active Learning Accelerates Ab Initio Molecular Dynamics on Pericyclic Reactive Energy Surfaces

2020 ◽  
Author(s):  
Shi Jun Ang ◽  
Wujie Wang ◽  
Daniel Schwalbe-Koda ◽  
Simon Axelrod ◽  
Rafael Gomez-Bombarelli
Keyword(s):  
Molecular Dynamics ◽  
Potential Energy ◽  
Transition State ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Energy Surface ◽  
Computational Cost ◽  
Reactive Trajectories ◽  
Dynamics Simulations ◽  
Energy Surfaces

<div>Modeling dynamical effects in chemical reactions, such as post-transition state bifurcation, requires <i>ab initio</i> molecular dynamics simulations due to the breakdown of simpler static models like transition state theory. However, these simulations tend to be restricted to lower-accuracy electronic structure methods and scarce sampling because of their high computational cost. Here, we report the use of statistical learning to accelerate reactive molecular dynamics simulations by combining high-throughput ab initio calculations, graph-convolution interatomic potentials and active learning. This pipeline was demonstrated on an ambimodal trispericyclic reaction involving 8,8-dicyanoheptafulvene and 6,6-dimethylfulvene. With a dataset size of approximately</div><div>31,000 M062X/def2-SVP quantum mechanical calculations, the computational cost of exploring the reactive potential energy surface was reduced by an order of magnitude. Thousands of virtually costless picosecond-long reactive trajectories suggest that post-transition state bifurcation plays a minor role for the reaction in vacuum. Furthermore, a transfer-learning strategy effectively upgraded the potential energy surface to higher</div><div>levels of theory ((SMD-)M06-2X/def2-TZVPD in vacuum and three other solvents, as well as the more accurate DLPNO-DSD-PBEP86 D3BJ/def2-TZVPD) using about 10% additional calculations for each surface. Since the larger basis set and the dynamic correlation capture intramolecular non-covalent interactions more accurately, they uncover longer lifetimes for the charge-separated intermediate on the more accurate potential energy surfaces. The character of the intermediate switches from entropic to thermodynamic upon including implicit solvation effects, with lifetimes increasing with solvent polarity. Analysis of 2,000 reactive trajectories on the chloroform PES shows a qualitative agreement with the experimentally-reported periselectivity for this reaction. This overall approach is broadly applicable and opens a door to the study of dynamical effects in larger, previously-intractable reactive systems.</div>

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

Nitro–Nitrite Isomerization and Transition State Switching in the Dissociation of Ionized Nitromethane: A Threshold Photoelectron–Photoion Coincidence Spectroscopy Study

2009 ◽  
Vol 15 (2) ◽  
pp. 157-166 ◽  
Author(s):  
Brandon Ferrier ◽  
Anne-Marie Boulanger ◽  
David M.P. Holland ◽  
David A. Shaw ◽  
Paul M. Mayer
Keyword(s):  
Transition State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Bond Cleavage ◽  
Cleavage Reaction ◽  
Nitrite Ion ◽  
Methyl Nitrite ◽  
Bond Cleavage Reaction ◽  
Entropy Of Activation ◽  
Lower Entropy

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been employed to investigate the competition between bond cleavage and rearrangement reactions in the dissociation of ionized nitromethane, 1. Modeling TPEPICO breakdown diagrams with a combination of RRKM theory and ab initio calculations at the G3 level of theory allowed the derivation of the activation energy for the isomerisation of 1 to ionized methyl nitrite, 2, 82 kJ mol−1. In addition, evidence was found for a transition state switch in the bond cleavage reaction in 1 leading to CH3• + NO2+. As internal energy increases, the effective transition state for this reaction becomes tighter (i.e. is characterized by a lower entropy of activation, Δ‡S). Fitted thresholds for NO+ and CH2OHO+ ions, originating from the isomeric methyl nitrite ion, are consistent with G3 level ab initio calculations.

Ab initio Cs transition state for the Diels-Alder reaction of acetylene and butadiene

1990 ◽  
Vol 55 (12) ◽  
pp. 3804-3807 ◽  
Author(s):  
James M. Coxon ◽  
Stephen T. Grice ◽  
Robert G. A. R. Maclagan ◽  
D. Quentin McDonald
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Alder Reaction ◽  
Diels Alder ◽  
Diels Alder Reaction
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