Abstract
Some conjugated polyenes have been examined using the valence-bond approximation including σ-bond compressional energy. The appropriate exchange and coulomb integrals were obtained as functions of bond length, using spectroscopic and thermal data for benzene and ethylene. These semi-empirical functions were then used in investigating linear cyclic polyenes. It was found that the bond lengths predicted for butadiene were in excellent agreement with experiment and that there should be appreciable bond alternation in longer chains. Similarly for n > 3, it was found that bonds should alternate in the cyclic polyenes C 2nH 2n and that the degree of bond alternation tends to increase with n. This agrees qualitatively with the recent application of simple molecular-orbital theory (including σ-bond compression) to long chain and large cyclic polyenes.
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