Ab Initio Calculations for Kinetic Modeling of Halocarbons

Berry, Rajiv; Schwartz, M.; Marshall, Paul

doi:10.1021/bk-1998-0677.ch018

Cited by 4 publications

(2 citation statements)

References 2 publications

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“…Haworth et al published a study on more than one hundred fluorinated C1 and C2 hydrofluorocarbon and oxidized hydrofluorocarbon molecules; both stable molecules and radicals. Berry et al , reported the negative errors in the calculated enthalpies by atomization; where the errors observed were linearly dependent upon the number of C–F bonds in the molecule. Wang et al , re-evaluated the enthalpy of formation of fluorinated hydrocarbons and also determined enthalpy of formation of fluorinated methyl peroxides using isodesmic work reactions with re-evaluated species.…”

Section: Introductionmentioning

confidence: 99%

Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical

2019

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Density functional theory (DFT) and composite ab initio based calculations are performed on trifluoroethane along with intermediate radicals, parent molecules of the radicals, and products related to the reaction of hydroxyl radical with 1,1,2-trifluoroethene, as a reference for hydrofluoroolefins (HFO). Potential energy barriers for internal rotations have been computed. Calculated torsional potentials are incorporated into the determination of entropy, S° 298, and heat capacities as a function of temperature, Cp (T), for each target molecule. Six isodesmic or isogyric reactions and five calculation methods are used to determine heats of formation at 298 K (Δf H 298) in kcal mol–1 of each target species. The CBS-APNO method shows the best agreement with experimental data in comparisons from 16 reference reactions on Δrxn H of each method. The lowest configuration structures of each target species are reported. Intramolecular hydrogen bonds between the hydroxyl hydrogen atom and the fluorine atom on the adjacent carbon can stabilize molecules by up to 3 kcal mol–1. R–OH bond dissociation energies are observed to increase with the number of fluorine atoms on the carbon connected to hydroxy group. Recommended Δf H 298 values in kcal mol–1 derived from the most stable conformers are CF2(OH)CH2F (−213.0), CF2(O•)CH2F (−148.6), CF2(OH)C•FH (−162.4), CHF2CHFOH (−207.5), CHF2C•FOH (−158.3), C•F2CHFOH (−155.5), CHF2CHFO• (−150.4), CF3CH2OH (−212.5), and CF3C•HOH (−167.9).

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Section: Introductionmentioning

confidence: 99%

Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical

2019

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“…Berry et al 71,72 applied various composite protocols and also the BAC-MP4 method to calculate heats of formation for fluoroethanes. The G2, G2(MP2), CBS-4, and CBS-Q model chemistries along with their bond additivity counterparts were invoked in these studies.…”

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High-Accuracy Theoretical Thermochemistry of Fluoroethanes

Nagy

Csontos

et al. 2014

J. Phys. Chem. A

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A highly accurate coupled-cluster-based ab initio model chemistry has been applied to calculate the thermodynamic functions including enthalpies of formation and standard entropies for fluorinated ethane derivatives, C2HxF6-x (x = 0-5), as well as ethane, C2H6. The invoked composite protocol includes contributions up to quadruple excitations in coupled-cluster (CC) theory as well as corrections beyond the nonrelativistic and Born-Oppenheimer approximations. For species CH2F-CH2F, CH2F-CHF2, and CHF2-CHF2, where anti/gauche isomerism occurs due to the hindered rotation around the C-C bond, conformationally averaged enthalpies and entropies at 298.15 K are also calculated. The results obtained here are in reasonable agreement with previous experimental and theoretical findings, and for all fluorinated ethanes except CH2FCH3 and C2F6 this study delivers the best available theoretical enthalpy and entropy estimates.

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Systematic errors in DFT calculations of haloalkane heats of formation

Cloud

Schwartz

2003

J Comput Chem

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The B3LYP and B3PW91 density functionals were employed with a large [BS1 = 6-311+G(3df,2p)] and small [BS2 = 6-311G(d,p)] basis set to compute enthalpies of formation (at optimized MP2/6-31G(d) geometries and with scaled HF/6-31G(d) frequencies) in the following series of haloalkanes: (1) the 15 fluoro-, chloro-, and chlorofluoromethanes, (2) the 18 fluorinated and chlorinated ethanes. Similar to earlier higher level calculations on haloalkanes, the computed enthalpies exhibited very large, systematic deviations from experiment. It was found that these errors could be largely eliminated using a very simple Bond Additivity Correction (BAC) formula, Delta(f)H degrees (BAC) = Delta(f)H degrees (calc) - n(CX). Delta(CX) [X = F, Cl], in which the BAC parameters, Delta(CF) and Delta(CCl) were determined by fitting the equation to experimental data on the four fluoroethanes and chloroethanes, respectively. The resultant BAC corrected enthalpies of formation are in excellent agreement with experiment, with RMS deviations in the same range as quoted RMS errors in measured enthalpies. Therefore, this simple BAC procedure may be utilized to provide reliable semiquantitative estimates of enthalpies of formation in larger haloalkanes, for which higher level ab initio calculations are not feasible.

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Ab Initio Calculations for Kinetic Modeling of Halocarbons

Cited by 4 publications

References 2 publications

Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical

Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical

High-Accuracy Theoretical Thermochemistry of Fluoroethanes

Systematic errors in DFT calculations of haloalkane heats of formation

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