Resonance in 1, 3-butadiene

Hyperconjugation in the above case may be regarded as an overlap of the ct orbital of the C—H bond and the n orbital of the C—C bond, analogous to the n-K orbital overlap previously considered. As might be expected, those who reject the idea of resonance in butadiene (p. 37) believe it even less likely when it involves nobond structures. 

We have not detected Feshbach resonances In butadiene or hexatrlene, and In general. It appears that such resonances are much weaker In larger hydrocarbons than In dl- and trlatomlc molecules... 

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