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Title: Theoretical C-H bond dissociation enthalpies for CH{sub 3}Br and CH{sub 2}ClBr

Abstract

The enthalpies of formation for the closed-shell molecules CH{sub 3}Br and CH{sub 2}ClBr, and the free radicals CH{sub 2}Br and CHClBr were estimated by ab initio molecular orbital computations using hydrogenation and isodesmic reactions as working chemical reactions. Four variants of theoretical approaches (levels) and three extended basis sets were applied in the calculations. The methods included fourth-order Moeller-Plesset perturbation theory (level 1), coupled-cluster theory (level 2), density functional theory (level 3), and Gaussian-2 (G2) theory (level 4). The standard enthalpies of formation values obtained at levels 1--4 for both the closed-shell and open-shell species agreed within {+-}1 kcal mol{sup {minus}1} irrespective of the working chemical reactions chosen. No basis set effects were observed. These invariances support the reliability of the computed data and are, for the most part, due to the cancellation of the computational errors as a result of the application of the working chemical reactions where the ab initio energies are combined with established experimental enthalpies of formation. The four methods provided enthalpies of formation values for CH{sub 3}Br, CH{sub 2}ClBr, and CH{sub 2}Br in good agreement with experimental values as well; the calculations supplied the first known enthalpy data for the ChClBr radical. The recommended standardmore » enthalpies of formation (at 298.15 K and 1.00 atm) are the unweighted averages of the results obtained at levels I-IV with the different hydrogenation and isodesmic reactions: CH{sub 3}Br, {minus}8.9 {+-} 0.8; CH{sub 2}ClBr, {minus}11.5 {+-} 1.1; CH{sub 2}Br, 40.7 {+-} 1.1; CHClBr, 35.1 {+-} 1.5 kcal mol{sup {minus}1}. The error limits designate the estimated maximal uncertainties. These enthalpies of formation values correspond to bond dissociation enthalpies of DH{sub 298}{degree}(BrH{sub 2}C-H) = 101.7 {+-} 1.4 kcal mol{sup {minus}1} and DH{sub 298}{degree}(BrClHC-H) = 98.7 {+-} kcal mol{sup {minus}1}.« less

Authors:
;
Publication Date:
Research Org.:
Univ. de Extremadura, Badajoz (ES)
OSTI Identifier:
20000059
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory
Additional Journal Information:
Journal Volume: 103; Journal Issue: 32; Other Information: PBD: 12 Aug 1999; Journal ID: ISSN 1089-5639
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; MOLECULAR ORBITAL METHOD; THEORETICAL DATA; ATMOSPHERIC CHEMISTRY; METHYL BROMIDE; HALOGENATED ALIPHATIC HYDROCARBONS; ENTHALPY; EXPERIMENTAL DATA; RADICALS

Citation Formats

Espinosa-Garcia, J., and Dobe, S. Theoretical C-H bond dissociation enthalpies for CH{sub 3}Br and CH{sub 2}ClBr. United States: N. p., 1999. Web. doi:10.1021/jp9834614.
Espinosa-Garcia, J., & Dobe, S. Theoretical C-H bond dissociation enthalpies for CH{sub 3}Br and CH{sub 2}ClBr. United States. doi:10.1021/jp9834614.
Espinosa-Garcia, J., and Dobe, S. Thu . "Theoretical C-H bond dissociation enthalpies for CH{sub 3}Br and CH{sub 2}ClBr". United States. doi:10.1021/jp9834614.
@article{osti_20000059,
title = {Theoretical C-H bond dissociation enthalpies for CH{sub 3}Br and CH{sub 2}ClBr},
author = {Espinosa-Garcia, J. and Dobe, S.},
abstractNote = {The enthalpies of formation for the closed-shell molecules CH{sub 3}Br and CH{sub 2}ClBr, and the free radicals CH{sub 2}Br and CHClBr were estimated by ab initio molecular orbital computations using hydrogenation and isodesmic reactions as working chemical reactions. Four variants of theoretical approaches (levels) and three extended basis sets were applied in the calculations. The methods included fourth-order Moeller-Plesset perturbation theory (level 1), coupled-cluster theory (level 2), density functional theory (level 3), and Gaussian-2 (G2) theory (level 4). The standard enthalpies of formation values obtained at levels 1--4 for both the closed-shell and open-shell species agreed within {+-}1 kcal mol{sup {minus}1} irrespective of the working chemical reactions chosen. No basis set effects were observed. These invariances support the reliability of the computed data and are, for the most part, due to the cancellation of the computational errors as a result of the application of the working chemical reactions where the ab initio energies are combined with established experimental enthalpies of formation. The four methods provided enthalpies of formation values for CH{sub 3}Br, CH{sub 2}ClBr, and CH{sub 2}Br in good agreement with experimental values as well; the calculations supplied the first known enthalpy data for the ChClBr radical. The recommended standard enthalpies of formation (at 298.15 K and 1.00 atm) are the unweighted averages of the results obtained at levels I-IV with the different hydrogenation and isodesmic reactions: CH{sub 3}Br, {minus}8.9 {+-} 0.8; CH{sub 2}ClBr, {minus}11.5 {+-} 1.1; CH{sub 2}Br, 40.7 {+-} 1.1; CHClBr, 35.1 {+-} 1.5 kcal mol{sup {minus}1}. The error limits designate the estimated maximal uncertainties. These enthalpies of formation values correspond to bond dissociation enthalpies of DH{sub 298}{degree}(BrH{sub 2}C-H) = 101.7 {+-} 1.4 kcal mol{sup {minus}1} and DH{sub 298}{degree}(BrClHC-H) = 98.7 {+-} kcal mol{sup {minus}1}.},
doi = {10.1021/jp9834614},
journal = {Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory},
issn = {1089-5639},
number = 32,
volume = 103,
place = {United States},
year = {1999},
month = {8}
}