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1998
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Research: Science and Education
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A Simple Molecular Orbital Treatment of the Barrier to Internal Rotation in the Ethane Molecule
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Derek W. Smith
University of Waikato, Department of Chemistry, Te Thare Wananga o Waikato, Private Bag 3105, Hamilton, New Zealand
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July 1998
Vol. 75 No. 7
p. 907
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| Abstract |
The origin of the barrier to internal rotation in the ethane molecule is explored in terms of elementary molecular orbital (MO) considerations. Emphasis is placed on the antibonding effect, i.e. the result that an antibonding MO is more destabilized than its bonding counterpart is stabilized, relative to the parent atomic orbitals (AOs). It is shown that, in the case of two equivalent AOs, this effect is approximately proportional to the square of the overlap integral. By constructing the ethane Mos from those of two methyl fragments, it is shown that the most important orbital energy changes consequent upon rotation about the C-C bond can be expressed in terms of the antibonding effect arising from the filled twofold-degenerate p-bonding and -antibonding MOs. This can be reduced to the dependence on the rotation angle of the vicinal H-H overlap integrals, which are calculated explicitly, showing that the antibonding effect is minimised in the staggered conformation.
See Letter re: this article.
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| More Information |
 Citation |
Smith, Derek W. J. Chem. Educ. 1998 75 907.
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Keywords |
Organic Chemistry, Physical Chemistry, Bonding Theory, MO Theory, Stereochemistry, Theoretical Chemistry
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History |
Created:
Last Updated: |
June 22, 1999
June 24, 2005
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Link to Letter added (April 2004).
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| Home > JCE Print > Journal of Chemical Education > Issues >
1998
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