The Effect of Conjugation on Electron Distribution

Conjugation affects not only the energies and conformations of organic molecules but also the distribution of the electrons. This has consequences on where the sites of highest charge are located, and on the polarities of molecules as manifest in such properties as the sites of ambident reactivity, dipole moments and the patterns in which they stack in crystals. 

If the carbonyl group is conjugated with a n bond, as in a,/3-unsaturated ketones, the fraction of positive charge on the carbon atom is shared with the n bond, and the (3 carbon becomes partly cationic in nature, as symbolised in Figs. 2.3 and 2.4 by the relatively small p orbitals on the (3 carbon atom in Li and ip2 of acrolein as a model for a Z-substituted alkene. Looking again at those pictures, it is clear that the sum of the coefficients of the filled p orbitals on the carbonyl carbon is smaller than the sum at the (3 carbon, and that 

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