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In the Classroom
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Cis and Trans Isomers of Cycloalkenes
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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. 1334
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| Abstract |
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As a rule, a trans disubstituted alkene is more stable than the corresponding
cis isomer. For cycloalkenes of fewer than eleven members, cis isomers are
more stable than their trans counterparts. Although this exception to the normal
rule is occasionally noted in beginning organic chemistry textbooks, it is
often done without a careful analysis of the reasons behind it. The purpose
of this article is to provide that analysis. In order for a cycloalkene to
accommodate a trans double bond one or more of the following nonideal geometries
must occur: a twisted π bond; pyramidal sp2-carbon atoms; nonideal sp3 bond
angles; or longer than normal C–C single and double bonds. This article provides
a list of experimentally determined relative energies of the cis and trans
isomers within the series cycloheptene–cycloundecene, along with computationally
derived energies at several levels of theory. It also examines the geometric
distortions through which cycloalkenes relieve the strain introduced by a trans
double bond.
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| Supplement |
Supplemental
materials include Spartan (.sxf) files, Protein Data Bank (.pdb) files of the optimized geometries (for use with Chem3D), Chime images, and Cartesian coordinates, along with instructions for downloading and viewing the files, all available.
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| More Information |
 Citation |
Barrows, Susan E.; Eberlein, Thomas H. J. Chem. Educ. 2005 82 1334.
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Keywords |
Alkenes; Computational Chemistry; Misconceptions / Discrepant Events; Molecular Modeling; Organic Chemistry; Second-Year Undergraduate; Upper-Division Undergraduate
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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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