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In the Classroom
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Understanding Rotation about a C=C Double Bond
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Susan E. Barrows and Thomas H. Eberlein
School of Science, Engineering, and Technology, Penn State Schuylkill, The Capital College, Schuylkill Haven, PA 17972
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September 2005
Vol. 82 No. 9
p. 1329
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| Abstract |
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In this article, twisting about the C=C double bond and the consequential pyramidalization
of sp2 carbon atoms in alkenes were examined in a molecular modeling study
using trans-2-butene as a model system. According to our trans-2-butene model
and other similar work, most of the strength of a π bond is retained upon twisting,
even for remarkably large C–C=C–C dihedral angles (up to 90°). The phenomenon
of sp2 carbon atom pyramidalization and preservation of π bond strength upon
twisting a C=C double bond is well established in the literature, but is rarely
discussed in introductory textbooks. This absence is noteworthy because profound
manifestations of this effect do occur in compounds that are covered in an
introductory organic chemistry curriculum. We present a simple method of introducing
the concept of a flexible C=C π bond into beginning organic chemistry courses.
We report the energetic demands of partial twisting about the C=C bond in 2-butene
as calculated using DFT, LMP2, and MCSCF methods. Finally, using the results
of these calculations, we assessed the degree of strain introduced by the twisted
nature of the C=C bond in trans cycloalkenes.
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| More Information |
 Citation |
Barrows, Susan E.; Eberlein, Thomas H. J. Chem. Educ. 2005 82 1329.
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Keywords |
Alkenes; Computational Chemistry; Misconceptions / Discrepant Events; Molecular Mechanics / Dynamics; Molecular Modeling; Organic Chemistry; Second-Year Undergraduate; Textbooks / Reference Books
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History |
Created:
Last Updated: |
August 2, 2005
August 10, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
2005
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September
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