Kinetics of the thermal decomposition of CF<sub>3</sub>CHCL<sub>2</sub> in a single‐pulse shock tube

Sekhar, M.V.C.; Millward, G.E.; Tschuikow‐Roux, E.

doi:10.1002/kin.550050307

Cited by 7 publications

(3 citation statements)

References 13 publications

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“…We now wish to present a study of chemically activated CD 3 CD 2 CHF 2 *; the 1,1-HF and 1,2-DF reactions can be identified, and the 1,1-HF reaction can be studied. The unimolecular 1,1-HX elimination reactions of dihalo- and trihalomethanes have been known for some time and continue to be of interest. − However, to our knowledge 1,1-HX elimination has been documented for only a limited number of 1,1-dihaloethanes, namely, CD 3 CHF 2 (the CF 2 CD 2 + HD product proposed in this paper can be explained by the recombination of CF 2 with CD 3 followed by the decomposition of vibrationally excited CD 3 CF 2 ) , CH 2 ClCDCl 2 , and CH 2 FCDF 2 , although the 1,1-HX channel has been assumed to be important for CF 3 CHF 2 , CF 2 ClCHF 2 , and CF 3 CHCl 2 . − Stabilization of the singlet carbene product by the halogen atom is required for 1,1-HX elimination to be competitive with 1,2-HX elimination from 1,1-dihaloalkanes. Other methods to generate carbenes in the gas phase are thermolysis and photolysis of diazirines and thermal rearrangement reactions of certain organosilane molecules, such as CF 3 CFX-SiF 3 and CHF 2 CFX-SiF 3 .…”

Section: Introductionmentioning

confidence: 89%

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Wormack¹,

McGreal²,

McClintock³

et al. 2015

J. Phys. Chem. A

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The recombination of CHF2 and C2D5 radicals was used to produce CD3CD2CHF2* molecules with 96 kcal mol(-1) of vibrational energy in a room temperature bath gas. The formation of CD3CD═CHF and CD3CD═CDF was used to identify the 1,2-DF and 1,1-HF unimolecular elimination channels; CD3CD═CDF is formed by isomerization of the singlet-state CD3CD2CF carbene. The total unimolecular rate constant is 1.6 × 10(6) s(-1), and the branching ratio for 1,1-HF elimination is 0.25. Threshold energies of 64 ± 2 and 73 ± 2 kcal mol(-1) were assigned to the 1,2-DF and 1,1-HF reaction channels. The E and Z isomers of 1-fluoropropene were observed for each reaction; approximately 30% of the CD3CD═CDF molecules derived from 1,1-HF elimination retained enough energy to undergo cis-trans isomerization. Electronic structure calculations with density-functional theory were used to characterize the transition-state structures and the H atom migration barrier for CD3CD2CF. Adjustment of the rate constants to account for kinetic-isotope effects suggest that the branching ratio would be 0.20 for 1,1-HF elimination from C2H5CHF2. The results from an earlier study of CD3CHF2 and CH3CHF2 are also reinterpreted to assign a threshold energy of 74 kcal mol(-1) for the 1,1-HF elimination reaction. Because CHF2CHF2* is generated in the photolysis system, the 1,1-and 1,2-HF-elimination reactions of CHF2CHF2* are discussed. The 1,1-HF channel was identified by trapping the CF2HCF carbene with cis-butene-2.

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Section: Introductionmentioning

confidence: 89%

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Wormack¹,

McGreal²,

McClintock³

et al. 2015

J. Phys. Chem. A

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“…The three-centered (aa) elimination of D X or H X has been observed from chemically activated CD3CHF2 [ 11, CHzClCDCl2 [2], and CHzFCDFz [3] and from shock heated CF&HzCl [4] and CF3CHC12 [5]. The aa process becomes competitive with the more common four-centered (ap) channel if the threshold energy for the aa channel is lowered by 1,l-dihalogen substitution or if the a@ threshold is elevated by some means.…”

Section: Introductionmentioning

confidence: 98%

Energy disposal in the three‐centered elimination of df from 1,1,2‐trifluoroethane‐1‐d₁

Holmes

Setser

Pritchard

1976

Int J of Chemical Kinetics

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The chemical activation data for three-and four-centered hydrogen fluoride elimination from CHtFCDFZ have been analyzed to assign the energy released to the olefin fragment in the three-centered process and to estimate the threshold energies for elimination channels. Based upon the cis-trans isomerization rates of CHF=CHF, 78% of the total available energy was released to the olefin fragment for the cra channel. The analysis suggests the existence of an appreciable barrier (-10 kcal/mole) for the reverse reaction, addition of the CHZFCF carbene to DF. The threshold energies for aa, a@, and @a elimination from 1, I ,2-trifluoroethane-1 -dl were assigned as 71, 68, and 68 kcal/mole, respectively. Analysis of the chemical activation data for 1,1,2,2,-tetrafluoroethane, without distinguishing between the three-and four-centered elimination channels, suggests a threshold energy of -75 kcai/mole.

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“…The characteristic unimolecular reaction pathway for haloalkanes is 1,2-HX (X = F, Cl, Br) elimination via a four-membered transition state. − However, the 1,1-HF or HCl elimination reaction pathway from 1,1-dihaloalkanes can compete with 2,1-HF or HCl elimination at high levels of vibrational energy or high temperature. − The 1,1-HX reaction requires a second halogen atom on the terminal carbon atom to stabilize the halocarbene product, which lowers the threshold energy, E 0 , for the 1,1-elimination reaction. Certain substituents can raise the threshold energy for 2,1-HX elimination, which has the effect of enhancing the 1,1-HX elimination component.…”

Section: Introductionmentioning

confidence: 99%

Chemical Activation Study of the Unimolecular Reactions of CD₃CD₂CHCl₂ and CHCl₂CHCl₂ with Analysis of the 1,1-HCl Elimination Pathway

et al. 2016

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Chemically activated C2D5CHCl2 molecules were generated with 88 kcal mol-1 of vibrational energy by the recombination of C2D5 and CHCl2 radicals in a room temperature bath gas. The competing 2,1-DCl and 1,1-HCl unimolecular reactions were identified by the observation of the CD3CD=CHCl and CD3CD=CDCl products. The initial CD3CD2C-Cl carbene product from 1,1-HCl elimination rearranges to CD3CD=CDCl under the conditions of the experiments. The experimental rate constants were 2.7 x107 and 0.47 x107 s-1 for 2,1-DCl and 1,1-HCl elimination reactions, respectively, which corresponds to branching fractions of 0.84 and 0.16. The experimental rate constants were compared to calculated statistical rate constants to assign threshold energies of 54 and ≈ 66 kcal mol-1 for the 1,2-DCl and 1,1-HCl reactions, respectively. The statistical rate constants were obtained from models developed from electronic-structure calculations for the molecule and its transition states. The rate constant (5.3 x 107 s-1) for the unimolecular decomposition of CHCl2CHCl2 molecules formed with 82 kcal mol-1 of vibrational energy by the recombination of CHCl2 radicals also is reported. Based upon the magnitude of the calculated rate constant, 1,1-HCl elimination must contribute less than 15% to the reaction; 1,2-HCl elimination is the major reaction and the threshold energy is 59 kcal mol-1. Calculations also were done to analyze previously published rate constants for chemically activated CD2Cl-CHCl2 molecules with 86 kcal mol-1 of energy in order to obtain a better overall description of the nature of the 1,1-HCl pathway for 1,1-dichloroalkanes. The interplay of the threshold energies for the 2,1-HCl and 1,1-HCl reactions and the available energy determines the product branching fractions for individual molecules. The unusual nature of the transition state for 1,1-HCl elimination is discussed.

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Kinetics of the thermal decomposition of CF₃CHCL₂ in a single‐pulse shock tube

Cited by 7 publications

References 13 publications

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Energy disposal in the three‐centered elimination of df from 1,1,2‐trifluoroethane‐1‐d₁

Chemical Activation Study of the Unimolecular Reactions of CD₃CD₂CHCl₂ and CHCl₂CHCl₂ with Analysis of the 1,1-HCl Elimination Pathway

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Kinetics of the thermal decomposition of CF3CHCL2 in a single‐pulse shock tube

Cited by 7 publications

References 13 publications

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD3CD2CHF2

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD3CD2CHF2

Energy disposal in the three‐centered elimination of df from 1,1,2‐trifluoroethane‐1‐d1

Chemical Activation Study of the Unimolecular Reactions of CD3CD2CHCl2 and CHCl2CHCl2 with Analysis of the 1,1-HCl Elimination Pathway

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Kinetics of the thermal decomposition of CF₃CHCL₂ in a single‐pulse shock tube

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DF Unimolecular Elimination Reactions of CD₃CD₂CHF₂

Energy disposal in the three‐centered elimination of df from 1,1,2‐trifluoroethane‐1‐d₁

Chemical Activation Study of the Unimolecular Reactions of CD₃CD₂CHCl₂ and CHCl₂CHCl₂ with Analysis of the 1,1-HCl Elimination Pathway