Application of the MO Method to 1,3-Butadiene

Exercise 21-1 Determine which of the following structures can be represented by one or more specific electron-pairing schemes similar to the Kekule structures of benzene  

To treat the 7r-electron system of 1,3-butadiene by simple MO theory, we combine the four p carbon orbitals of an atomic-orbital model, such as 17, to obtain four molecular orbitals  

21 The Resonance and Molecular-Orbital Methods and Their Applications. Pericyclic Reactions 

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