Theoretical studies of decomposition kinetics of CF3CCl2O radical (original) (raw)
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Theoretical studies on decomposition kinetics of CF3CF2O radical
Indian Journal of Chemistry Sect a Inorganic Physical Theoretical Analytical, 2010
The unimolecular decomposition reactions of CF 3 CF 2 O radical formed from hydrofluorocarbons, CF 3 CHF 2 in the atmosphere has been investigated using ab initio quantum mechanical methods. Two most important channels of decomposition occurring via CC bond scission and F-elimination have been considered. Energetics calculations have been performed at G2(MP2) and G2M(CC,MP2) level of theories. The calculations reveal that CC bond scission is the dominant pathway during the decomposition of CF 3 CF 2 O radical. Transition states have been searched on the potential energy surface of the decomposition reactions involved. Intrinsic reaction coordinate calculations have also been made. The analysis shows that transition states smoothly connect the reactant and products. The thermal rate constants for the decomposition reactions involved are evaluated using Canonical transition state theory utilizing the ab initio data at 298 K and 1 atm pressure.
Thermal decomposition of CF3CFClO radical – A computational study
Indian Journal of Chemistry Section a
A theoretical study on the decomposition pathways of haloalkoxy radical formed from 2-chloro-1,1,1,2-tetrafluoroethane has been reported. Structures of all the reactants, products and transition states involved in the decomposition pathways have been optimized and characterized at MP2(full)/6-31G(d,p) level of theory. Single point energy calculations have been performed using MP4, QCISD(T) and CCSD(T) levels of theory. Critical energy barriers have been calculated for C-C bond scission and Cl elimination, the two prominent decomposition channels considered in the present investigation, and found to be 8.4 and 1.5 kcal mol -1 respectively. Results show that Cl elimination is the dominant path involving a lower barrier height. Using transition state theory, rate constants for the decomposition pathways, viz., Cl-elimination and C-C bond scission, calculated at 298 K and 1 atm pressure are found to be 4.6×10 5 and 5.1×10 4 s -1 , respectively. The existence of transition states on the corresponding potential energy surface has been ascertained by performing Intrinsic Reaction Coordinate calculations.
Ab initio studies on the decomposition kinetics of CF3OCF2O radical
Journal of Molecular Modeling, 2011
The present study deals with the decomposition of CF 3 OCF 2 O radical formed from a hydrofluoroether, CF 3 OCHF 2 (HFE-125), in the atmosphere. The study is performed using ab initio quantum mechanical methods. Two plausible pathways of decomposition of the titled species have been considered, one involving C-O bond scission and the other occurring via F atom elimination. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2M(CC,MP2) level of theory. Out of the two prominent decomposition channels considered, the C-O bond scission is found to be dominant involving a barrier height of 15.3 kcal mol −1 whereas the Felimination path proceeds with a barrier of 26.1 kcal mol −1 . The thermal rate constants for the above two decomposition pathways are evaluated using canonical transition state theory (CTST) and these are found to be 1.78×10 6 s −1 and 2.83×10 −7 s −1 for C-O bond scission and F-elimination respectively at 298 K and 1 atm pressure. Transition states are searched on the potential energy surfaces involved during the decomposition channels and each of the transition states is characterized. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.
Computational study on decomposition kinetics of CH 3 CFClO radical
Journal of Chemical Sciences, 2011
The present study deals with the decomposition of haloalkoxy radical (CH 3 CFClO) formed from 1,1-dichloro-1-fluoroethane in the atmosphere. The study is performed using ab-initio quantum mechanical methods. Out of the three plausible pathways of decomposition of the titled species, the one that involved the C-C bond scission and the other occurring via Cl-atom elimination have been considered for detailed study. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at MP2 level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2(MP2) level of theory. The path involving the Cl-elimination is found to be dominant and found to occur with a barrier height of 3.6 kcal mol −1 whereas the C-C bond scission path proceeds with a barrier of 10.0 kcal mol −1 . The thermal rate constants for the above two decomposition pathways are evaluated using Canonical Transition State Theory (CTST) and these are found to be 2.9 × 10 8 s −1 and 4.3 × 10 5 s −1 for Cl-elimination and C-C bond scission respectively at 298 K and 1 atm. pressure. The existence of transition states on the corresponding potential energy surface is ascertained by the occurrence of only one imaginary frequency obtained during the frequency calculation. The Intrinsic Reaction Coordinate (IRC) calculation has also been performed to confirm the smooth connection of the TS to the reactant and the products.
Ab Initio Study on the Thermal Decomposition of CH3CF2O Radical
Bulletin of the Korean Chemical Society, 2009
The decomposition reaction mechanism of CH3CF2O radical formed from hydroflurocarbon, CH3CHF2 (HFC-152a) in the atmosphere has been investigated using ab-initio quantum mechanical methods. The geometries of the reactant, products and transition states involved in the decomposition pathways have been optimized and characterized at DFT-B3LYP and MP2 levels of theories using 6-311++G(d,p) basis set. Calculations have been carried out to observe the effect of basis sets on the optimized geometries of species involved. Single point energy calculations have been performed at QCISD(T) and CCSD(T) level of theories. Out of the two prominent decomposition channels considered viz., CC bond scission and F-elimination, CC bond scission is found to be the dominant path involving a barrier height of 12.3 kcal/mol whereas the F-elimination path involves that of a 28.0 kcal/mol. Using transition-state theory, rate constant for the most dominant decomposition pathway viz., CC bond scission is calculated at 298 K and found to be 1.3 × 10 4 s-1. Transition states are searched on the potential energy surfaces involving both decomposition channels and each of the transition states are characterized. The existence of transition states on the corresponding potential energy surface are ascertained by performing Intrinsic Reaction Coordinate (IRC) calculation.
Computational study on the thermal decomposition and isomerization of the CH 3 OCF 2 O • radical
Canadian Journal of Chemistry, 2012
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 b-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 × 10 4 s -1 at 298 K and 1 atm (1 atm = 101.325 kPa).
Journal of Molecular Modeling, 2010
Hydrofluoroethers are being considered as potential candidates for third generation refrigerants. The present investigation involves the ab initio quantum mechanical study of the decomposition mechanism of CF 3 OCH 2 O radical formed from a hydrofluoroether, CF 3 OCH 3 (HFE-143a) in the atmosphere. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at the DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Energy calculations have been performed at the G2(MP2) and G2M (CC,MP2) level of theory. Two prominent decomposition channels, C-O bond scission and reaction with atmospheric O 2 have been considered for detailed investigation. Studies performed at the G2(MP2) level reveals that the decomposition channel involving C-O bond scission occurs with a barrier height of 23.8 kcal mol −1 whereas the oxidative pathway occurring with O 2 proceeds with an energy barrier of 7.2 kcal mol −1 . On the other hand the corresponding values at G2M(CC,MP2) are 24.5 and 5.9 kcal mol −1 respectively. Using canonical transition state theory (CTST) rate constants for the two pathways considered are calculated at 298 K and 1 atm pressure and found to be 5.9×10 −6 s −1 and 2.3×10 −5 s −1 respectively. The present study concludes that reaction with O 2 is the dominant path for the consumption of CF 3 OCH 2 O in the atmosphere. Transition states are searched and characterized on the potential energy surfaces involved in both of the reaction channels. The existence of transition state on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.
Journal of Fluorine Chemistry, 2018
The mechanisms and kinetics of the hydrogen abstraction reactions from two structural isomers, CF3CF2CH2CH2F and CF3CH2CH2CF3 (HFC-356mff), by OH radicals are investigated by quantum chemical methods along with SCTST theory. The structures of the reactants, transition states, products and hydrogen-bonded complexes are optimized by the KMLYP density functional theory method. The energies of the stationary points are also evaluated by M05-2X, M06-2X and MPWB1K methods for the purpose of comparison. The computed barrier heights and the corresponding rate coefficients are slightly affected by the quantum-chemical method. The significance of the tunnel effect and vibrational anharmonicities in predicting the rate coefficients are also investigated. The present theoretical computations predicts the atmospheric lifetimes of the CF3CF2CH2CH2F and CF3CH2CH2CF3 are about 1.00 and 6.56 years, respectively.