The performance of the IMOMO and IMOHC integrated methods in predicting geometry, frequency and energy of reaction and activation in hydrogen abstraction reactionsElectronic supplementary information (ESI) available: tables of calculated harmonic vibrational frequencies for all stationary points, reactants, products and saddle points, at the single and integrated levels (a total of 147 calculations). See http://www.rsc.org/suppdata/cp/b1/b109961m/

2002 ◽  
Vol 4 (10) ◽  
pp. 1807-1814 ◽  
Author(s):  
J. Espinosa-García
Keyword(s):  
Hydrogen Abstraction ◽  
Saddle Points ◽  
Vibrational Frequencies ◽  
Stationary Points ◽  
Supplementary Information ◽  
Integrated Methods

Dual-level direct dynamics study on the hydrogen abstraction reaction of fluorine atom with 1,1-difluoro-1-chloroethane

2011 ◽  
Vol 89 (11) ◽  
pp. 1396-1402 ◽  
Author(s):  
Li Wang ◽  
Song Liu ◽  
Hongqing He ◽  
Jinglai Zhang
Keyword(s):  
Reaction Path ◽  
Hydrogen Abstraction ◽  
Single Point ◽  
Minimum Energy ◽  
State Theory ◽  
Stationary Points ◽  
Kinetic Properties ◽  
Direct Dynamics ◽  
Wide Range ◽  
Major Reaction

The kinetic properties of the reaction of F atoms with CH2H′CF2Cl are investigated by a dual-level direct dynamics method. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path (MEP) are obtained at the MPW1K/6–311+G(d,p) level of theory. Two complexes with energy less than that of the reactants are located in the two reactant paths, respectively. The energy profiles of two reactions are refined with the interpolated single-point energies (ISPE) method at the G3(MP2)/MPW1K level. The rate constants are evaluated using the canonical variational transition state theory (CVT) with a small-curvature tunneling correction (SCT) over a wide range of temperature 200–2000 K. Agreement between the calculated CVT/SCT rate constant and the experimental value is good at 295 K. Our calculations show that the reaction path CH2H′CF2Cl + F → CH2CF2Cl + H′F (Ra) is the major reaction path below 400 K. Moreover, the contribution of CH2H′CF2Cl + F → CHH′CF2Cl + HF (Rb) to the whole reaction increases with the temperature increasing and exceeds path Ra to be the major reaction path.

scholarly journals Locating and Characterizing the Stationary Points of the Extended Rosenbrock Function

2009 ◽  
Vol 17 (3) ◽  
pp. 437-453 ◽  
Author(s):  
Schalk Kok ◽  
Carl Sandrock
Keyword(s):  
Random Search ◽  
Saddle Points ◽  
Relative Magnitude ◽  
Negative Eigenvalue ◽  
High Dimensionality ◽  
Stationary Points ◽  
Particle Swarm Algorithm ◽  
Initial Population ◽  
Arbitrary Precision ◽  
Newtonian Method

Two variants of the extended Rosenbrock function are analyzed in order to find the stationary points. The first variant is shown to possess a single stationary point, the global minimum. The second variant has numerous stationary points for high dimensionality. A previously proposed method is shown to be numerically intractable, requiring arbitrary precision computation in many cases to enumerate candidate solutions. Instead, a standard Newtonian method with multi-start is applied to locate stationary points. The relative magnitude of the negative and positive eigenvalues of the Hessian is also computed, in order to characterize the saddle points. For dimensions up to 100, only two local minimizers are found, but many saddle points exist. Two saddle points with a single negative eigenvalue exist for high dimensionality, which may appear as “near” local minima. The remaining saddle points we found have a predictable form, and a method is proposed to estimate their number. Monte Carlo simulation indicates that it is unlikely to escape these saddle points using uniform random search. A standard particle swarm algorithm also struggles to improve upon a saddle point contained within the initial population.

scholarly journals Chemical insights into the atmospheric oxidation of thiophene by hydroperoxyl radical

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Maryam Seyed Sharifi ◽  
Hamed Douroudgari ◽  
Morteza Vahedpour
Keyword(s):  
Rate Constants ◽  
Potential Energy Surfaces ◽  
Hydrogen Abstraction ◽  
State Theory ◽  
Stationary Points ◽  
Positive Temperature ◽  
Oxidation Reactions ◽  
Hydroperoxyl Radical ◽  
Title Reaction ◽  
High Level

AbstractThe reaction mechanisms and kinetics of thiophene oxidation reactions initiated by hydroperoxyl radical, and decomposition of the related intermediates and complexes, have been considered herein by using high-level DFT and ab initio calculations. The main energetic parameters of all stationary points of the suggested potential energy surfaces have been computed at the BD(T) and CCSD(T) methods, based on the geometries optimized at the B3LYP/6-311 + g(d,p) level of theory. Rate constants of bimolecular reactions (high-pressure limit rate constants) at temperatures from 300 to 3000 K for the first steps of the title reaction have been obtained through the conventional transition state theory (TST), while the pressure dependent rate constants and the rate constants of the second and other steps have been calculated employing the Rice–Ramsperger–Kassel–Marcus/Master equation (RRKM/ME). The results show that the rate constants of addition to α and β carbons have positive temperature dependence and negative pressure dependence. It is found that the additions of HO2 to the α and β carbons of thiophene in the initial steps of the title reaction are the most favored pathways. Also, the addition to the sulfur atom has a minor contribution. But, all efforts for simulating hydrogen abstraction reactions have been unsuccessful. In this complex oxidation reaction, about 12 different products are obtained, including important isomers such as thiophene-epoxide, thiophene-ol, thiophene-oxide, oxathiane, and thiophenone. The calculated total rate constants for generation of all minimum stationary points show that the addition reactions to the α and β carbons are the fastest among all at temperatures below 1000 K, while the proposed multi-step parallel reactions are more competitive at temperatures above 1200 K. Furthermore, important inter-and intra-molecular interactions for some species have been investigated by two well-known quantum chemistry method, the NBO and AIM analyses. Thermochemical properties such as free energy, enthalpy, internal energy, and entropy for thiophene and hydroperoxyl radical and related species in the simulated reactions have been predicted using a combination of the B3LYP and BD(T) methods.

Sign in / Sign up

Export Citation Format

Share Document