A kinetic study of the reactions of OH radicals with fluoroethanes. Estimates of C—H bond strengths in fluoroalkanes

Martin, J. G.; Paraskevopoulos, G.

doi:10.1139/v83-155

Cited by 43 publications

(23 citation statements)

References 12 publications

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“…In addition, the error bars do not overlap. However, the source of the discrepancy can be easily identified, it is the auxiliary heat of formation data of CF 3 –CH 2 F. The currently accepted value, –906.2 ± 3.2 kJ/mol, differs by −10.4 kJ/mol from that used in ref . After recalculating Δ f H 298 ° (CF 3 –CHF) with this auxiliary value one can arrive at −691.1 ± 5.3 kJ/mol which agrees well with our result.…”

Section: Resultssupporting

confidence: 88%

“…CH 3 −CHF. In 1983 Martin and Paraskevopoulos investigated the kinetics of reactions that took place between OH radicals and fluoroethanes, 48 and for Δ f H 298 °(CH 3 −CHF) − 78.2 ± 6.7 kJ/mol was derived. Four years later Tschuikow and Salomon 49 studied the photobromation of C 2 H 5 Cl, and analyzing the kinetics and thermochemical data of related compounds they got a somewhat higher value, −74.1 ± 4.6 kJ/ mol, for Δ f H 298 °(CH 3 −CHF).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Martin and Paraskevopoulos studied the reaction of OH and fluoroethanes and derived a −680.7 ± 9.6 kJ/mol value for Δ f H 298 ° (CF 3 –CHF). They observed that the C–H bond dissociation energies, D C–H , of alkanes and fluoroalkanes correlate with the logarithm of k / n , where k is the rate constant for the reaction and n is the number of hydrogens in the alkane or fluoroalkane.…”

Section: Resultsmentioning

confidence: 99%

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Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

2017

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An accurate coupled-cluster (CC) based model chemistry was applied to calculate reliable thermochemical quantities for hydrofluorocarbon derivatives including radicals 1-fluoroethyl (CH-CHF), 1,1-difluoroethyl (CH-CF), 2-fluoroethyl (CHF-CH), 1,2-difluoroethyl (CHF-CHF), 2,2-difluoroethyl (CHF-CH), 2,2,2-trifluoroethyl (CF-CH), 1,2,2,2-tetrafluoroethyl (CF-CHF), and pentafluoroethyl (CF-CF). The model chemistry used contains iterative triple and perturbative quadruple excitations in CC theory, as well as scalar relativistic and diagonal Born-Oppenheimer corrections. To obtain heat of formation values with better than chemical accuracy perturbative quadruple excitations and scalar relativistic corrections were inevitable. Their contributions to the heats of formation steadily increase with the number of fluorine atoms in the radical reaching 10 kJ/mol for CF-CF. When discrepancies were found between the experimental and our values it was always possible to resolve the issue by recalculating the experimental result with currently recommended auxiliary data. For each radical studied here this study delivers the best heat of formation as well as entropy data.

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Section: Resultssupporting

confidence: 88%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

2017

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“…However, the reaction enthalpy for reaction R1 can be estimated from the enthalpies of formation for reactants and products: ∆H f°( OH • ) ) 9.4, 9 ∆H f°( H 2 O) ) -57.8, 9 ∆H f°( CH 3 CH 2 F) ) -62.9, 10 and ∆H f°( CH 3 CHF • ) ) -18.7 ( 1.6 kcal mol -1 . 11 ∆H f°( CH 3 CHF • ) is calculated from ∆H f°( CH 3 CH 2 F) ) -62.9, 10 ∆H f°( H • ) ) 52.1, 12 and the bond dissociation energy D e (CH 3 CHF-H) ) 96.3 kcal mol -1 , which is estimated 11 from an empirical correlation between the rate constants of alkane and haloalkane reactions with OH radical and their C-H bond dissociation energies. The estimated reaction enthalpy (-23.0 kcal mol -1 ) for reaction R1 is in a fair agreement with the calculated value at the G2 level of theory.…”

Section: A Optimized Structures and Vibration Frequenciesmentioning

confidence: 99%

An ab Initio Study on Reactivity of Fluoroethane with Hydroxyl Radical: Application of G2 Theory

Sekušak¹,

Güsten²,

Sabljić³

1996

J. Phys. Chem.

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The reaction of fluoroethane with hydroxyl radical has been investigated by ab initio molecular orbital theory, and two possible reaction pathways were examined, R and abstractions. Optimized geometries and harmonic vibrational frequencies have been calculated for reactants, products, and transition states up to the (U)MP2/ 6-31G(d,p) level of theory. Accurate energies of reactants, products, and transition states are obtained using G2 theory. The calculated barrier height and reaction enthalpy of R abstraction are 1.35 and -18.36 kcal mol -1 , respectively. A very good agreement is found with available experimental data. Two rotamers were found as the transition-state structures involved in the abstraction reaction. This reaction has higher barrier heights, 2.66 and 3.73 kcal mol -1 , respectively, and it is less exothermic than R abstraction, with reaction enthalpy of -14.42 kcal mol -1 . One rotamer is stabilized by the delocalization of electrons from a fluorine atom into the O-H bond. The transition-state interactions between reacting units have been analyzed in terms of the natural bond orbital (NBO) method. The main delocalization process for all transition-state structures seems to be between the oxygen nonbonding orbitals and the NBOs of the reactive C(1)-H(3) bond. The results on fluoroethane reactivity with hydroxyl radical have been compared with previous results on chloroethane and ethane. The influence of halogen substitution on the barrier heights and reaction enthalpies has been rationalized in terms of three different effects: the electron density redistribution in the reactive C(1)-H(3) bond, the stabilization of radical product, and the participation of halogen atom in breaking the reactive C(1)-H(3) bond. Finally, the C-H bond dissociation energies of fluoroethane and chloroethane have been calculated at G2, UMP4, and UMP2/6-311+G(2d,p)//UMP2/6-31G(d,p) levels of theory as well as the G2 enthalpies of formation of R-and -fluoroethyl radicals since the experimental values are not available yet.

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“…No comprehensive unified treatment of all the three reactions was made and comparisons with the experiments were selective. [20][21][22][23][24] On the other hand, the detailed kinetics of HFCs in combustion environments, by contrast, has not been subject to extensive experimental investigation due to lack of proper measurement methods for flame inhibition chemistry. [25][26][27][28] At present, the synchrotron radiation-molecular beam mass spectrometry (SR-MBMS) techniques have been successfully used in studying hydrocarbon combustion and proven to be befitting and powerful tools in flame chemistry.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive Theoretical and Experimental Studies on the CF₃H Fire‐extinguishing Mechanism

Zhou

2011

Chin. J. Chem.

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In order to clarify the chemical suppression mechanisms of CF3H, experimental and theoretical studies were conducted respectively in this paper. Firstly, the combustion species in low pressure laminar premixed flat methane flames with CF3H addition is measured by synchrotron radiation molecular beam mass spectrometry (SR‐MBMS) experimentally. Fire suppression chemistry of CF3H is investigated by selective detection of combustion radicals and intermediates in experimental process. Secondly, quantum chemistry calculations are performed to calculate the potential energy surfaces (PES) for the CF3H unimolecular dissociation reaction and reactions of CF3H with free radical OH and H at the B3LYP/6‐311++G** and QCISD(T)/6‐311++G** levels. Finally, the chemical suppression mechanism of CF3H was discussed by comparing the theoretical calculation with experimental measurement.

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A kinetic study of the reactions of OH radicals with fluoroethanes. Estimates of C—H bond strengths in fluoroalkanes

Cited by 43 publications

References 12 publications

Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

An ab Initio Study on Reactivity of Fluoroethane with Hydroxyl Radical: Application of G2 Theory

Comprehensive Theoretical and Experimental Studies on the CF₃H Fire‐extinguishing Mechanism

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A kinetic study of the reactions of OH radicals with fluoroethanes. Estimates of C—H bond strengths in fluoroalkanes

Cited by 43 publications

References 12 publications

Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

Accurate Theoretical Thermochemistry for Fluoroethyl Radicals

An ab Initio Study on Reactivity of Fluoroethane with Hydroxyl Radical: Application of G2 Theory

Comprehensive Theoretical and Experimental Studies on the CF3H Fire‐extinguishing Mechanism

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Product

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Comprehensive Theoretical and Experimental Studies on the CF₃H Fire‐extinguishing Mechanism