ABSTRACT
This chapter discusses dienes and alkene–ketones, alkene–aldehydes, or alkene–esters with a particular emphasis on those molecules that are conjugated. Conjugated dienes react similarly to other alkenes, but due to conjugation the carbocation or radical intermediates formed from conjugated dienes are resonance-stabilized. Therefore, there are two sites of reactivity: the carbonyl as well as the C=C unit and so there are differences in product distribution when compared to simple alkenes. There is a well-known reaction of conjugated carbonyl compounds in which a nucleophile adds to the C=C unit. The nomenclature and identification of conjugated and nonconjugated dienes is straightforward. The chemical reactions of such compounds are more complicated. In addition to the acyclic compounds just discussed, it is common to see cyclic molecules with conjugated p-bonds. An important cyclic diene is cyclopenta-1,3-diene. The reaction of the C=C unit of the conjugated system as a Bronsted–Lowry base, involves donation of electrons to the acidic proton.
