Even Monocyclic Polyenes Aromaticity and Antiaromaticity Hiickels Rule

10 Even Monocyclic Polyenes Aromaticity and Antiaromaticity Hiickel s Rule 

Let us return to a problem that baffled us earlier (Section 3.7), i.e., the estimation of n energies of cyclic polyenes. 

Both 1,3,5-hexatriene and benzene can be formed by union of two allyl radicals. 

Allyl is an odd AH in which the NBMO coefficients can be found at once by Longuet-Higgins rule  

The two n energies of union can now be found from equation (3.24), remembering that the n energy of simultaneous union of two odd AHs at two points is a sum of the two individual unions, 

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