skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Conformations and barriers of haloethyl radicals (CH{sub 2}XCH{sub 2}, X = F, Cl, Br, I): Ab initio studies

Abstract

Radicals such as CH{sub 2}XCH{sub 2}{sm{underscore}bullet}, where X is a halogen, play an important role in the stereochemical control observed in many chemical reactions. To elucidate the origin of the stereoselectivity, the authors calculated the structures and potential energy surfaces of the haloethyl radicals (CH{sub 2}XCH{sub 2}{sm{underscore}bullet}, X = F, Cl, Br, I) using ab initio quantum mechanics [HF, local MP2, DFT (both B3PW91) and (B3LYP)]. The CH{sub 2}BrCH{sub 2}{sm{underscore}bullet} and CH{sub 2}ICH{sub 2}{sm{underscore}bullet} radicals strongly favor the symmetrically bridged structures while the CH{sub 2}ClCH{sub 2}{sm{underscore}bullet} radical leads to similar energy for symmetric bridging and classical structures. (In contrast, X = H and F leads to dramatically different structures.) This confirms the Skell hypothesis of symmetric bridging to explain the stereochemical control of the CH{sub 2}BrCH{sub 2}{sm{underscore}bullet} and CH{sub 2}ICH{sub 2}{sm{underscore}bullet} radicals, indicating that such bridged structures play an important role in the dissociation processes involving CH{sub 2}XCH{sub 2}{sm{underscore}bullet} with X = Cl, Br, and I. The trends in the rotational barriers and structural parameters are consistent with hyperconjugation between the singly occupied carbon 2p orbital and the {sigma}*(C-X) MO. The authors find that the rotational barrier, bridged structure, and dissociation of the radicals are described much more accurately usingmore » DFT (with GGA) than with HF or LMP2.« less

Authors:
; ;
Publication Date:
Research Org.:
California Inst. of Tech., Pasadena, CA (US)
Sponsoring Org.:
National Science Foundation (NSF); US Department of the Air Force; US Department of the Navy, Office of Naval Research (ONR); USDOE
OSTI Identifier:
20003185
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: 33; Other Information: PBD: 19 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; RADICALS; MATHEMATICAL MODELS; HALOGEN COMPOUNDS; ETHYL RADICALS; STEREOCHEMISTRY

Citation Formats

Ihee, H., Zewail, A.H., and Goddard, W.A. III. Conformations and barriers of haloethyl radicals (CH{sub 2}XCH{sub 2}, X = F, Cl, Br, I): Ab initio studies. United States: N. p., 1999. Web. doi:10.1021/jp990867n.
Ihee, H., Zewail, A.H., & Goddard, W.A. III. Conformations and barriers of haloethyl radicals (CH{sub 2}XCH{sub 2}, X = F, Cl, Br, I): Ab initio studies. United States. doi:10.1021/jp990867n.
Ihee, H., Zewail, A.H., and Goddard, W.A. III. Thu . "Conformations and barriers of haloethyl radicals (CH{sub 2}XCH{sub 2}, X = F, Cl, Br, I): Ab initio studies". United States. doi:10.1021/jp990867n.
@article{osti_20003185,
title = {Conformations and barriers of haloethyl radicals (CH{sub 2}XCH{sub 2}, X = F, Cl, Br, I): Ab initio studies},
author = {Ihee, H. and Zewail, A.H. and Goddard, W.A. III},
abstractNote = {Radicals such as CH{sub 2}XCH{sub 2}{sm{underscore}bullet}, where X is a halogen, play an important role in the stereochemical control observed in many chemical reactions. To elucidate the origin of the stereoselectivity, the authors calculated the structures and potential energy surfaces of the haloethyl radicals (CH{sub 2}XCH{sub 2}{sm{underscore}bullet}, X = F, Cl, Br, I) using ab initio quantum mechanics [HF, local MP2, DFT (both B3PW91) and (B3LYP)]. The CH{sub 2}BrCH{sub 2}{sm{underscore}bullet} and CH{sub 2}ICH{sub 2}{sm{underscore}bullet} radicals strongly favor the symmetrically bridged structures while the CH{sub 2}ClCH{sub 2}{sm{underscore}bullet} radical leads to similar energy for symmetric bridging and classical structures. (In contrast, X = H and F leads to dramatically different structures.) This confirms the Skell hypothesis of symmetric bridging to explain the stereochemical control of the CH{sub 2}BrCH{sub 2}{sm{underscore}bullet} and CH{sub 2}ICH{sub 2}{sm{underscore}bullet} radicals, indicating that such bridged structures play an important role in the dissociation processes involving CH{sub 2}XCH{sub 2}{sm{underscore}bullet} with X = Cl, Br, and I. The trends in the rotational barriers and structural parameters are consistent with hyperconjugation between the singly occupied carbon 2p orbital and the {sigma}*(C-X) MO. The authors find that the rotational barrier, bridged structure, and dissociation of the radicals are described much more accurately using DFT (with GGA) than with HF or LMP2.},
doi = {10.1021/jp990867n},
journal = {Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory},
number = 33,
volume = 103,
place = {United States},
year = {1999},
month = {8}
}