Conjugate Nucleophilic Addition
With α,β unsaturated carbonyl compounds (also called conjugated enones), some nucleophiles will approach and bond to the β-carbon, such as amines, cyanide, and Gilman reagents. Normally with aldehydes and ketones, a nucleophile will only approach and bond to the carbonyl carbon. Being in a polar bond with oxygen, carbonyl carbons are electropositive. However, with an α,β unsaturated carbonyl compound, the positive charge arising due to the polarity of the carbonyl group is shared between the carbonyl carbon and the β-carbon by means of allylic resonance. This is why the β-carbon of α,β unsaturated carbonyl compounds is attractive to nucleophiles.