Hiickel calculations enamines

Whereas the allyl anion, with a plane of symmetry through the central atom, has a node at that atom in j/ j, amides, esters, enamines, enol ethers and enolate ions do not have a node precisely on the central atom. Taking planar A V-dimethylviny-lamine and the enolate of acetaldehyde as examples, simple Hiickel calculations give the n orbitals in Fig. 2.15, which includes the allyl anion for comparison. 

Fig. 2.15 n Orbital energies and coefficients from simple Hiickel calculations of the allyl anion, enamine and enolate ion (orbital energies in kJ moP1 relative to a)... 

Dienamines differ from simple enamines in that (i) there is an additional nucleophilic site at the -position and (ii) an equilibrium mixture of three isomeric dienamines is frequently formed, consisting of the linear s-trans isomer 1, the linear s-cis isomer 2 and the cross-conjugated isomer 31 (Scheme 1). A variety of factors influence the outcome of electrophilic attack on such an equilibrium system. Hiickel molecular orbital calculations indicate a significantly higher electron density at the -positions compared to the -positions of the dienamine system2 (Figure 1). 

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