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Cis and Trans Isomerization in Cyclic Alkenes: A Topic for Discovery Using the Results of Molecular Modeling

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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

J. Chem. Educ., 2004, 81 (10), p 1529

DOI: 10.1021/ed081p1529

Publication Date (Web): October 1, 2004

Section:

History, Education, and Documentation

Abstract

Beginning organic chemistry students are often taught the generalizations that alkenes are planar and that cis alkenes are less stable than their trans isomers. An exception to these rules occurs in cycloalkenes of fewer than eleven members, wherein cis isomers are more stable then their trans counterparts. This article describes an activity in which students are led to discover the fundamental reasons behind the unusual instability of the trans isomers in medium-sized cycloalkenes by using the results of molecular modeling. Notably, students will make the unexpected discovery that twisting about π bonds is perhaps more facile than they had been led to believe. Furthermore, such twisting is invariably accompanied by pyramidalization of the ostensibly "planar" sp² carbon atoms, which helps to maintain p-orbital overlap and π-bond strength. Thus, this molecular modeling-based exercise helps drive home the point that alkenes need not be planar.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Organic Chemistry

Keywords (Feature):

Teaching with Technology

Keywords (Pedagogy):

Collaborative / Cooperative Learning

Keywords (Subject):

Covalent Bonding

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This article has been cited by 3 ACS Journal articles (3 most recent appear below).

Pyrolysis of Aryl Sulfonate Esters in the Absence of Solvent: E1 or E2? A Puzzle for the Organic Laboratory
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Journal of Chemical Education2008 85 (4), 552
- Pyrolysis of Aryl Sulfonate Esters in the Absence of Solvent: E1 or E2? A Puzzle for the Organic Laboratory
  John J. Nash , Marnie A. Leininger and Kurt Keyes
  Journal of Chemical Education2008 85 (4), 552
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Understanding Rotation about a C=C Double Bond
Susan E. Barrows and Thomas H. Eberlein
Journal of Chemical Education2005 82 (9), 1329
- Understanding Rotation about a C=C Double Bond
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  Journal of Chemical Education2005 82 (9), 1329
  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 ...
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Cis and Trans Isomers of Cycloalkenes
Susan E. Barrows and Thomas H. Eberlein
Journal of Chemical Education2005 82 (9), 1334
- Cis and Trans Isomers of Cycloalkenes
  Susan E. Barrows and Thomas H. Eberlein
  Journal of Chemical Education2005 82 (9), 1334
  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 ...
  Abstract | Hi-Res PDF | PDF w/ Links