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  Home > JCE Print > Journal of Chemical Education > Issues > 1998  > May  >
Research: Science and Education
The Pi-Electron-System of Monocyclic Polyenes C2nH2n with Alternating Single and Double Bonds
J. J. C. Mulder
Gorlaeus Laboratories, Leiden Institute of Chemistry, P.O. Box 9502, 2300 RA Leiden, THE NETHERLANDS
Cover
May 1998
Vol. 75 No. 5
p. 594
Abstract
On the basis of quantum chemical calculations and general theoretical arguments a discussion has been going on regarding the stability towards distortion of benzene and the monocyclic polyene C2nH2n in general. Also the polyene radicals C2n+1H2n+3, of which the allyl- radical is the first representative, are of interest. These molecules contain a {sigma}-skeleton and a {pi}-electron system with two main contributing and, in a symmetric geometry, equivalent resonance structures. The question asked is whether (in)stability towards distortion away from a symmetric geometry is a {pi}-electron property or, on the contrary, primarily connected to the {sigma}-skeleton. In this communication the question is answered firstly by means of simple molecular orbital and valence bond arguments in the case of the {pi}-electron system, and secondly with the characteristic difference between 2p{pi} - and 2p{sigma} overlap integrals for the discussion of the {sigma}-skeleton. The outcome is inescapable: notwithstanding the symmetrizing influence of resonance, the {pi}-electron system as a whole is unstable towards distortion.
More Information
*  Citation
 Mulder, J. J. C. J. Chem. Educ. 1998 75 594.
*  Keywords
 Organic Chemistry, History/Philosophy, Physical/Theoretical
*  History
 Created:
Last Updated:		 June 23, 1999
June 24, 2005
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