Elucidation of structure–reactivity relationships in hindered phenols via quantum chemistry and transition state theory

2007 ◽  
Vol 62 (18-20) ◽  
pp. 5232-5239 ◽  
Author(s):  
Jim Pfaendtner ◽  
Linda J. Broadbelt
Keyword(s):  
Quantum Chemistry ◽  
Transition State ◽  
Transition State Theory ◽  
State Theory ◽  
Hindered Phenols

Theoretical Study on the Reaction of Et3GeCH=CH2 with Et3SiOH

2012 ◽  
Vol 549 ◽  
pp. 301-304
Author(s):  
Xin Cheng Chen ◽  
Xiao Yun Han ◽  
Wan Yong Ma ◽  
Li Gang Gai
Keyword(s):  
Quantum Chemistry ◽  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Theoretical Study ◽  
State Theory ◽  
Arrhenius Behavior ◽  
Variational Transition State Theory ◽  
Temperature Range ◽  
Variational Transition State

The reaction of Et3GeCH=CH2 + Et3SiOH → Et3SiO–Ge–Et3 + CH2=CH2 has been studied using quantum chemistry methods. Geometries of reactants, transition states, and products have been optimized respectively at the b3lyp/6-311+g(2d,2p) level. The rate constants were evaluated using canonical variational transition state theory (CVT) and canonical variational transition state theory with small-curvaturetunneling contributions (CVT/SCT) over the temperature range of 200-3500K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior, and a three-parameter rate-temperature formula has been fitted as follows: k(T)=1.43×10-38T 5.41exp(-13200/T) (in units of cm3 molecule-1s-1).

scholarly journals Atmospheric oxidation reactions of imidazole initiated by hydroxyl radicals: kinetics and mechanism of reactions and atmospheric implications

2019 ◽  
Vol 21 (16) ◽  
pp. 8445-8456 ◽  
Author(s):  
Zahra Safaei ◽  
Abolfazl Shiroudi ◽  
Ehsan Zahedi ◽  
Mika Sillanpää
Keyword(s):  
Quantum Chemistry ◽  
Transition State ◽  
Reaction Kinetics ◽  
Hydroxyl Radicals ◽  
Transition State Theory ◽  
Oxidation Mechanism ◽  
State Theory ◽  
Atmospheric Oxidation ◽  
Oxidation Reactions ◽  
Quantum Chemistry Calculations

The atmospheric oxidation mechanism of imidazole initiated by hydroxyl radicals is investigated via OH-addition and H-abstraction pathways by quantum chemistry calculations at the M06-2X/aug-cc-pVTZ level of theory coupled with reaction kinetics calculations using statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory and transition state theory (TST).

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.

Bimolecular Reactions, Transition-State Theory

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Transition State ◽  
Saddle Point ◽  
Transition State Theory ◽  
Classical Mechanics ◽  
Small Degree ◽  
State Theory ◽  
Reaction Coordinate ◽  
Partition Functions ◽  
Bimolecular Reactions ◽  
Activated Complex

This chapter discusses an approximate approach—transition-state theory—to the calculation of rate constants for bimolecular reactions. A reaction coordinate is identified from a normal-mode coordinate analysis of the activated complex, that is, the supermolecule on the saddle-point of the potential energy surface. Motion along this coordinate is treated by classical mechanics and recrossings of the saddle point from the product to the reactant side are neglected, leading to the result of conventional transition-state theory expressed in terms of relevant partition functions. Various alternative derivations are presented. Corrections that incorporate quantum mechanical tunnelling along the reaction coordinate are described. Tunnelling through an Eckart barrier is discussed and the approximate Wigner tunnelling correction factor is derived in the limit of a small degree of tunnelling. It concludes with applications of transition-state theory to, for example, the F + H2 reaction, and comparisons with results based on quasi-classical mechanics as well as exact quantum mechanics.

Quasiclassical Trajectory and Transition State Theory Studies of the N(4S) + H2↔ NH(X3Σ-) + H Reaction

2002 ◽  
Vol 106 (16) ◽  
pp. 4125-4136 ◽  
Author(s):  
Ronald Z. Pascual ◽  
George C. Schatz ◽  
Gÿorgÿ Lendvay ◽  
Diego Troya
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
State Theory
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