Theoretical study on the reaction of atomic oxygen with unsymmetrical dimethylhydrazine

2013 ◽  
Vol 91 (5) ◽  
pp. 315-319 ◽  
Author(s):  
Jinmiao Wen ◽  
Yafang Tian ◽  
Hongqing He ◽  
Li Wang
Keyword(s):  
Rate Constants ◽  
Room Temperature ◽  
Theoretical Study ◽  
Single Point ◽  
State Theory ◽  
Stationary Points ◽  
Energy Profiles ◽  
Unsymmetrical Dimethylhydrazine ◽  
Increasing Temperature ◽  
Dynamics Method

A dual-level direct dynamics method is employed to study the reaction mechanism of (CH3)2NNH2 (unsymmetrical dimethylhydrazine) with the oxygen (O) atom. The geometries and frequencies of all the stationary points are optimized at the MPW1K/6-311G (d, p) level, and the energy profiles are further refined by the interpolated single-point energies (ISPE) method at the BMC-CCSD level of theory. The rate constants of the O atom with (CH3)2NNH2 are evaluated over a wide temperature range of 200–2000 K by using the canonical variational transition-state theory (CVT) with the small curvature tunneling correction (SCT). The agreement between the theoretical and experimental rate constants is good around room temperature. The channels of H abstraction from the -NH2 position favor temperatures below 1200 K. With increasing temperature, contributions from other channels should be taken into account. The reactivity of N2H4, CH3NHNH2, and (CH3)2NNH2 toward atomic O is compared to explore the methylation effect.

Dual-Level Direct Dynamics Studies on the Hydrogen Abstraction Reactions of CH2CH3 - n Xn+HBr (X=Cl, Br and n=1, 2)

2012 ◽  
Vol 65 (2) ◽  
pp. 160
Author(s):  
Li Wang ◽  
Jianxiang Zhao ◽  
Hongqing He ◽  
Jinglai Zhang
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Single Point ◽  
State Theory ◽  
Stationary Points ◽  
Variational Transition State Theory ◽  
Point Energy ◽  
Direct Dynamics ◽  
Variational Transition State

The reactions of the HBr molecule with CH2CH2Cl (reaction R1), CH2CHCl2 (R2), CH2CH2Br (R3) and CH2CHBr2 (R4) are investigated by a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points were calculated at the MPW1K/6–311+G(d,p) and BMK/6–311+G(d,p) levels. To refine the reaction enthalpy and energy barrier height of each reaction, single-point energy calculations were carried out by the G2M(RCC5) method based on the geometries optimized at the above-mentioned two levels. Using the canonical variational transition state theory or the canonical variational transition state theory with the small-curvature tunneling correction, the rate constants of HBr with CH2CH2Cl (R1), CH2CHCl2 (R2), CH2CH2Br (R3), and CH2CHBr2 (R4) were calculated over a wide temperature range of 200–2000 K at the G2M(RCC5)//MPW1K/6–311+G(d,p) level. The effect of chlorine or bromine substitution on the ethyl radical reactivity is discussed. Finally, the total rate constants are fitted by two models, i.e. three-parameter and four-parameter expressions.

DIRECT AB INITIO DYNAMICS STUDIES ON THE REACTION OF METHANETHIOL WITH CHLORINE ATOMS

2010 ◽  
Vol 09 (01) ◽  
pp. 265-277 ◽  
Author(s):  
YONG-XIA WANG ◽  
XUE-MEI DUAN ◽  
QIN WANG ◽  
LI WANG ◽  
JING-YAO LIU ◽  
...  
Keyword(s):  
Rate Constants ◽  
Single Point ◽  
Negative Temperature ◽  
State Theory ◽  
Stationary Points ◽  
Sh Group ◽  
Reaction Channels ◽  
Point Calculation ◽  
Experimental Values ◽  
Cl Atoms

The reaction of CH3SH with Cl atoms has been theoretically studied using dual-level direct dynamics method. Three reaction channels, two H-abstraction (from the –SH and –CH3 groups) and one substitution channel, have been found. The optimized geometries and frequencies of all the stationary points are calculated at the MP2/6-311+G(d,p) level, and the potential-energy profile along each reaction path is refined by the single-point calculation at the CCSD(T)/6-311+G(d,p) level. The rate constants for the two H-abstraction channels are evaluated by the improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling (SCT) correction over a wide temperature range of 193–1000 K. The calculated ICVT/SCT rate constants are in good agreement with available experimental values and exhibit negative temperature dependence below 500 K. The present calculations indicate that the H-abstraction from the –SH group is the major channel for the title reaction, while the H-abstraction from the –CH3 group should be taken into account only at high temperatures.

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.

Theoretical study on the chemical formation mechanism of a β-myrcene ozonolysis reaction under atmospheric conditions

2012 ◽  
Vol 90 (8) ◽  
pp. 708-715 ◽  
Author(s):  
Yuyang Zhao ◽  
Jing Bai ◽  
Chenxi Zhang ◽  
Chen Gong ◽  
Xiaomin Sun
Keyword(s):  
Rate Constants ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Single Point ◽  
State Theory ◽  
Tunneling Effect ◽  
Atmospheric Conditions ◽  
Functional Theory ◽  
Real Atmosphere ◽  
Energy Surfaces

Density functional theory (DFT) was used to study the β-myrcene ozonolysis reaction. The reactants, intermediates, transition states, and products were optimized at the MPWB1K/6–31G(d,p) level. The single-point energies were performed at the MPWB1K/6–311+G(3df,2p) level. The profiles of the potential energy surfaces were constructed and the rate constants of the reaction steps were analyzed. The possible reaction mechanisms for the ozonolysis intermediates in real atmosphere are also discussed. Based on quantum chemistry information, the rate constants were calculated using Rice–Ramsperger–Kassel–Marcus (RRKM) theory and the canonical variational transition-state theory (CVT) with small curvature tunneling effect (SCT). Arrhenius equations of rate constants over the temperature range of 200–800 K are provided, and the lifetimes of the reaction species in the troposphere were estimated according to rate constants.

Computational study on the reaction of atomic chlorine with 1,2-dibromoethane (CH2BrCH2Br)

2013 ◽  
Vol 91 (11) ◽  
pp. 1123-1129 ◽  
Author(s):  
Ang-yang Yu
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Computational Study ◽  
Minimum Energy ◽  
State Theory ◽  
Basis Set ◽  
Stationary Points ◽  
Variational Transition State Theory ◽  
Variational Transition State

In this work, the reaction mechanism and kinetics of Cl + CH2BrCH2Br → products are theoretically investigated for the first time. The optimized geometries and frequencies of all of the stationary points and selected points along the minimum-energy path for the three hydrogen abstraction channels and two bromine abstraction channels are calculated at the BH&H-LYP level with the 6-311G** basis set and the energy profiles are further calculated at the CCSD(T) level of theory. The rate constants are evaluated using the conventional transition-state theory, the canonical variational transition-state theory, and the canonical variational transition-state theory with a small-curvature tunneling correction over the temperature range 200–1000 K. The results show that reaction channel 3 is the primary channel and the calculated rate constants are in good agreement with available experimental values. The three-parameter Arrhenius expression for the total rate constants over 200–1000 K is provided.

Kinetics and mechanism for chlorine-initiated atmospheric oxidation of ethyl formate

2014 ◽  
Vol 92 (7) ◽  
pp. 598-604 ◽  
Author(s):  
Yan Zhao ◽  
Xiaomin Sun ◽  
Wenxing Wang ◽  
Laixiang Xu
Keyword(s):  
Rate Constants ◽  
Density Functional ◽  
Single Point ◽  
Oxidation Mechanism ◽  
Density Functional Theory Method ◽  
Ethyl Formate ◽  
Stationary Points ◽  
Atmospheric Conditions ◽  
Point Energy ◽  
Rearrangement Reaction

The chlorine-initiated reaction mechanism of ethyl formate in the atmosphere was investigated using the density functional theory method. The geometry parameters and frequencies of all of the stationary points were calculated at the B3LYP/ 6-31G(d,p) level. The single-point energy calculations were carried out at different levels, including MP2/6-31G(d), MP2/6-311++G(d,p), and CCSD(T)/6-31G(d). A detailed oxidation mechanism is provided and discussed. Present results show that α-ester rearrangement reaction and the O2 direct abstraction from IM6 (HC(O)OCH(O)CH3) are the more favorable pathway and are competitive. The 1,4-H shift isomerization of IM6 proved to be feasible under general atmospheric conditions. The decomposition of IM18 (CH3CH2OC(O)O) is favorable both thermodynamically and kinetically. Canonical variational transition theory with small-curvature tunneling correction was employed to predict the rate constants. The overall rate constant of ethyl formate at 298 K is 8.63 × 10−12 cm3 molecule−1 s−1. The Arrhenius equations of rate constants at the temperature range of 200–380 K were fitted.

Theoretical study on the reaction mechanism of vinyl acetate with OH radicals in the atmosphere

2013 ◽  
Vol 91 (4) ◽  
pp. 241-247 ◽  
Author(s):  
Yan Zhao ◽  
Haitao Sun ◽  
Renjun Wang ◽  
Fei Gao
Keyword(s):  
Vinyl Acetate ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Theoretical Study ◽  
Single Point ◽  
Density Functional Theory Method ◽  
Basis Sets ◽  
Stationary Points ◽  
Oh Radicals ◽  
Point Energy

The reaction mechanisms of vinyl acetate with OH radicals in the atmosphere have been studied using the density functional theory method. The geometry parameters and frequencies of all of the stationary points are calculated at the MPWB1K level with the 6-31G(d,p) basis sets. The single-point energy calculations are carried out at the MPWB1K/6-311+G(3df,2pd) level. The detailed profiles of the potential energy surfaces for the reactions are constructed. Two OH addition and three H abstraction reaction pathways are considered for the reaction of vinyl acetate with OH radicals. The theoretical study shows that the most energetically favorable isomer is that of OH addition to the terminal carbon positions (C1 atom). The α-ester rearrangement, which is characteristic of ester oxidation processes, is confirmed to be thermodynamically and kinetically favorable. The main products of the OH-initiated atmospheric oxidation of vinyl acetate are formaldehyde, formic acetic anhydride, and acetic acid.

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 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.

scholarly journals Theoretical study of the addition and hydrogen abstraction reactions of the methyl radical with formaldehyde and hydroxymethylene

2018 ◽  
Vol 83 (10) ◽  
pp. 1113-1122
Author(s):  
Huu Nguyen ◽  
Xuan Nguyen
Keyword(s):  
Transition State Theory ◽  
Energy Surface ◽  
Theoretical Study ◽  
Hydrogen Abstraction ◽  
Single Point ◽  
State Theory ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radical ◽  
Variational Transition State Theory ◽  
Kinetics Of

The mechanism, thermochemistry and kinetics of the addition and hydrogen-atom abstraction reactions of the methyl radical with formaldehyde and hydroxymethylene were investigated by ab initio calculations. The potential energy surface (PES) of the reactions were calculated by single point calculations at the CCSD(T)/6-311++G(3df,2p) level based on geometries at the B3LYP/6-311++G(3df,2p) level. The rate constants of various product channels were estimated by the variational transition state theory (VTST) and are discussed for the seven reactions in the temperature range of 300?2000 K and at 101325 Pa pressure. The calculated results showed that all the hydrogen abstraction reactions are more favorable than the addition ones.

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