Computational study on the thermal decomposition and isomerization of the CH3OCF2O• radical

2012 ◽  
Vol 90 (4) ◽  
pp. 403-409 ◽  
Author(s):  
Hari Ji Singh ◽  
Bhupesh Kumar Mishra ◽  
Pradeep Kumar Rao
Keyword(s):  
Transition State Theory ◽  
Computational Study ◽  
Single Point ◽  
State Theory ◽  
Basis Set ◽  
Point Energy ◽  
B3lyp Level ◽  
Bond Scission ◽  
Decomposition Pathway ◽  
Thermal Rate Constant

The geometries of the reactant, products, and transition states involved in the decomposition pathways of the CH3OCF2O• radical formed during the photooxidation of CH3OCHF2 (HFE-152a) have been optimized and characterized at the DFT-B3LYP level of theory using the 6–311G(d,p) basis set. Single-point energy calculations have been made at the G2M (CC,MP2) level of theory. Out of the four prominent decomposition channels considered, the β-C–O bond scission is found to be the dominant path involving a barrier height of 9.78 kcal mol–1 (1 cal = 4.184 J). The thermal rate constant for the above decomposition pathway is evaluated using canonical transition state theory (CTST) and was found to be 5.27 × 104 s–1 at 298 K and 1 atm (1 atm = 101.325 kPa).

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.

scholarly journals Computational Study of the Dissociation Reactions of Secondary Ozonide

Atmosphere ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 100 ◽  
Author(s):  
Mansour H. Almatarneh ◽  
Shefa’ F. Alrebei ◽  
Mohammednoor Altarawneh ◽  
Yuming Zhao ◽  
Abd Al-Aziz Abu-Saleh
Keyword(s):  
Barrier Height ◽  
Computational Study ◽  
Reaction Pathway ◽  
Single Point ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Water Molecules ◽  
Point Energy ◽  
Secondary Ozonide

This contribution presents a comprehensive computational study on the reactions of secondary ozonide (SOZ) with ammonia and water molecules. The mechanisms were studied in both a vacuum and the aqueous medium. All the molecular geometries were optimized using the B3LYP functional in conjunction with several basis sets. M06-2X, APFD, and ωB97XD functionals with the full basis set were also used. In addition, single-point energy calculations were performed with the G4MP2 and G3MP2 methods. Five different mechanistic pathways were studied for the reaction of SOZ with ammonia and water molecules. The most plausible mechanism for the reaction of SOZ with ammonia yields HC(O)OH, NH3, and HCHO as products, with ammonia herein acting as a mediator. This pathway is exothermic and exergonic, with an overall barrier height of only 157 kJ mol−1 using the G3MP2 method. All the reaction pathways between SOZ and water molecules are endothermic and endergonic reactions. The most likely reaction pathway for the reaction of SOZ with water involves a water dimer, in which the second water molecule acts as a mediator, with an overall barrier height of only 135 kJ mol−1 using the G3MP2 method. Solvent effects were found to incur a significant reduction in activation energies. When the second H2O molecule acts as a mediator in the reaction of SOZ with water, the barrier height of the rate-determining step state decreases significantly.

scholarly journals Application of one-dimensional semiclassical transition state theory to the CH 3 OH + H ⇌ CH 2 OH/CH 3 O + H 2 reactions

2018 ◽  
Vol 376 (2115) ◽  
pp. 20170147 ◽  
Author(s):  
Xiao Shan ◽  
David C. Clary
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Single Point ◽  
Computational Cost ◽  
State Theory ◽  
Reverse Direction ◽  
Point Energy ◽  
One Dimensional ◽  
Theory Calculation

The rate constants of the two branches of H-abstractions from CH 3 OH by the H-atom and the corresponding reactions in the reverse direction are calculated using the one-dimensional semiclassical transition state theory (1D SCTST). In this method, only the reaction mode vibration of the transition state (TS) is treated anharmonically, while the remaining internal degrees of freedom are treated as they would have been in a standard TS theory calculation. A total of eight ab initio single-point energy calculations are performed in addition to the computational cost of a standard TS theory calculation. This allows a second-order Richardson extrapolation method to be employed to improve the numerical estimation of the third- and fourth-order derivatives, which in turn are used in the calculation of the anharmonic constant. Hindered-rotor (HR) vibrations are identified in the equilibrium states of CH 3 OH and CH 2 OH, and the TSs of the reactions. The partition function of the HRs are calculated using both a simple harmonic oscillator model and a more sophisticated one-dimensional torsional eigenvalue summation (1D TES) method. The 1D TES method can be easily adapted in 1D SCTST computation. The resulting 1D SCTST with 1D TES rate constants show good agreement to previous theoretical and experimental works. The effects of the HR on rate constants for different reactions are also investigated. This article is part of the theme issue ‘Modern theoretical chemistry’.

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.

Theoretical study on NO3-initiated oxidation of acenaphthene in the atmosphere

2008 ◽  
Vol 86 (2) ◽  
pp. 129-137 ◽  
Author(s):  
Xiaohui Qu ◽  
Qingzhu Zhang ◽  
Wenxing Wang
Keyword(s):  
Product Information ◽  
Environmental Concern ◽  
Single Point ◽  
Basis Set ◽  
Orbital Theory ◽  
Night Time ◽  
Point Energy ◽  
Secondary Reactions ◽  
Favorable Reaction ◽  
High Level

Acenaphthene is widespread and toxic, and thus of substantial environmental concern. The reaction with NO3 radicals is an important atmospheric loss process of acenaphthene at night time. In this work, the mechanism for the NO3-initiated atmospheric oxidation reaction of acenaphthene has been studied using high level molecular orbital theory. Geometries of all the related species have been optimized at the MPWB1K level with the 6–31G(d,p) basis set. The single-point energy calculations have been carried out at the MPWB1K/6–311+G(3df,2p) level. The possible secondary reactions were also studied. Several energetically favorable reaction pathways were revealed for the first time.Key words: acenaphthene, NO3 radicals, reaction mechanism, product information, oxidation degradation.

scholarly journals Computational Modeling and Theoretical Calculations on the Interactions between Spermidine and Functional Monomer (Methacrylic Acid) in a Molecularly Imprinted Polymer

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Yujie Huang ◽  
Qiujin Zhu
Keyword(s):  
Binding Energy ◽  
Methacrylic Acid ◽  
Molecularly Imprinted Polymer ◽  
Single Point ◽  
Basis Set ◽  
Stable Complex ◽  
Functional Monomer ◽  
Imprinted Polymer ◽  
Point Energy ◽  
Molecularly Imprinted

This paper theoretically investigates interactions between a template and functional monomer required for synthesizing an efficient molecularly imprinted polymer (MIP). We employed density functional theory (DFT) to compute geometry, single-point energy, and binding energy (ΔE) of an MIP system, where spermidine (SPD) and methacrylic acid (MAA) were selected as template and functional monomer, respectively. The geometry was calculated by using B3LYP method with 6-31+(d) basis set. Furthermore, 6-311++(d, p) basis set was used to compute the single-point energy of the above geometry. The optimized geometries at different template to functional monomer molar ratios, mode of bonding between template and functional monomer, changes in charge on natural bond orbital (NBO), and binding energy were analyzed. The simulation results show that SPD and MAA form a stable complex via hydrogen bonding. At 1 : 5 SPD to MAA ratio, the binding energy is minimum, while the amount of transferred charge between the molecules is maximum; SPD and MAA form a stable complex at 1 : 5 molar ratio through six hydrogen bonds. Optimizing structure of template-functional monomer complex, through computational modeling prior synthesis, significantly contributes towards choosing a suitable pair of template-functional monomer that yields an efficient MIP with high specificity and selectivity.

Theoretical study on the OH-initiated atmospheric reaction of N-methyl perfluorobutane sulfonamidoethanol (C4F9SO2N(CH3)CH2CH2OH)

2013 ◽  
Vol 91 (12) ◽  
pp. 1161-1167
Author(s):  
Juan Dang ◽  
Lei Ding ◽  
Xiaoyan Sun ◽  
Qingzhu Zhang ◽  
Wenxing Wang
Keyword(s):  
Reaction Mechanism ◽  
Degradation Products ◽  
Single Point ◽  
Basis Set ◽  
Stationary Points ◽  
Geometrical Parameters ◽  
Chemical Transformations ◽  
Point Energy ◽  
Range Transport ◽  
Perfluorinated Carboxylic Acids

N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE), a new product of the 3M Company, is currently widely used in many countries and territories. It is prone to volatilize to the atmosphere where it can undergo long-range transport and chemical transformations. In this work, the reaction mechanism for the OH-initiated atmospheric oxidation of NMeFBSE was investigated. The geometrical parameters and vibrational frequencies of all of the stationary points were calculated at the MPWB1K level with the 6-31G+(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level. The results indicate that the channel of the formation of C4F9 and HSO3N(CH3)CH2CH2OH resulting from OH addition to NMeFBSE and hydrogen abstractions from the −CH3 group in NMeFBSE are energetically favorable. The main degradation products include perfluorinated carboxylic acids (C3F7COOH, C2F5COOH, CF3COOH), HSO3N(CH3)CH2CH2OH, NMeFBSA (C4F9SO2NH(CH3)), C4F9SO2N(CH3)CH2CHO, and C4F9SO2N(CH3)CH2COOH. The reaction mechanism for the formation of NMeFBSA is reported for the first time. Using the atmospheric fate of NMeFBSE as a guide, it seems that N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the atmosphere.

Atmospheric oxidation mechanism of polyfluorinated sulfonamides — A quantum chemical and kinetic study

2013 ◽  
Vol 91 (6) ◽  
pp. 472-478 ◽  
Author(s):  
Xiaoyan Sun ◽  
Lei Ding ◽  
Qingzhu Zhang ◽  
Wenxing Wang
Keyword(s):  
Rate Constants ◽  
Density Functional ◽  
Single Point ◽  
Oxidation Mechanism ◽  
Basis Set ◽  
Atmospheric Oxidation ◽  
Oh Radicals ◽  
Oh Radical ◽  
Orbital Theory ◽  
Point Energy

Polyfluorinated sulfonamides (FSAs, F(CF2)nSO2NR1R2) are present in the atmosphere and may serve as the source of perfluorocarboxylates (PFCAs, CF3(CF2)nCOO–) in remote locations through long-range atmospheric transport and oxidation. Density functional theory (DFT) molecular orbital theory calculations were carried out to investigate OH radical-initiated atmospheric oxidation of a series of sulfonamides, F(CF2)nSO2NR1R2 (n = 4, 6, 8). Geometry optimizations of the reactants as well as the intermediates, transition states, and products were performed at the MPWB1K level with the 6-31G+(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level of theory. The OH radical-initiated reaction mechanism is given and confirms that the OH addition to the sulfone double bond producing perfluoroalkanesulfonic acid directly cannot occur in the general atmosphere. Canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution was used to predict the rate constants. The overall rate constants were determined, k(T) (N-EtFBSA + OH) = (3.21 × 10−12) exp(–584.19/T), k(T) (N-EtFHxSA + OH) = (3.21 × 10−12) exp(–543.24/T), and k(T) (N-EtFOSA + OH) = (2.17 × 10−12) exp(–504.96/T) cm3 molecule−1 s−1, over the possible atmospheric temperature range of 180–370 K, indicating that the length of the F(CF2)n group has no large effect on the reactivity of FSAs. Results show that the atmospheric lifetime of FSAs determined by OH radicals will be 20–40 days, which agrees well with the experimental values (20–50 days), 20 thus they may contribute to the burden of perfluorinated pollution in remote regions.

Quantum chemical study on the atmospheric photooxidation of ethyl acetate

2014 ◽  
Vol 92 (9) ◽  
pp. 814-820 ◽  
Author(s):  
Yan Zhao ◽  
Xiaomin Sun ◽  
Wenxing Wang ◽  
Laixiang Xu
Keyword(s):  
Acetic Anhydride ◽  
Ethyl Acetate ◽  
Density Functional ◽  
Single Point ◽  
Quantum Chemical Study ◽  
Density Functional Theory Method ◽  
Basis Set ◽  
Oh Radicals ◽  
Point Energy ◽  
Rearrangement Reaction

The mechanism for OH radical initiated atmospheric photoxidation reaction of ethyl acetate was carried out by using the density functional theory method. Geometries have been optimized at the B3LYP level with a standard 6-31G(d,p) basis set. The single-point energy calculations have been performed at the MP2/6-31G(d), MP2/6-311++G(d,p), and CCSD(T)/6-31G(d) levels, respectively. All of the possible degradation channels involved in the oxidation of ethyl acetate by OH radicals have been presented and discussed. Among the five possible hydrogen abstraction pathways of the reaction of ethyl acetate with OH radicals, the hydrogen abstractions from the C1–H3 and C2–H5 bonds are the dominant reaction pathways due to the low potential barriers and strong exothermicity. The β-ester rearrangement of IM6 is energetically favorable but is not expected to be important. The α-ester rearrangement reaction and O2 direct abstraction from IM17 are the more favorable pathways and are strongly competitive. In addition, the α-ester rearrangement reaction is confirmed to be a one-step process. Acetic acid, formic acetic anhydride, acetoxyacetaldehyde, and acetic anhydride are the main products for the reaction of ethyl acetate with OH radicals.

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