Conjugate additions occur only when the C=C double bond is immediately adjacent to the C=O group. They don’t occur to C=C bonds that aren’t conjugated . Compounds with double bonds adjacent to a C=O group are known as α,β-unsaturated carbonyl compounds. Many α,β-unsaturated carbonyl compounds have trivial names, and some are shown here. Some classes of α,β-unsaturated carbonyl compounds also have names such as ‘enone’, made up of ‘ene’ (for the double bond) + ‘one’ (for ketone).

Most types of nucleophiles can be made to undergo conjugate additions with α,β-unsaturated carbonyl compounds, and seven examples are shown below. Note that many of these nucleophiles would not add to a simple carbonyl group: we will explain why shortly. Conjugate addition is also known as Michael addition, and the reactive α,β-unsaturated carbonyl compounds shown here are often known as Michael acceptors.

The reason that α,β-unsaturated carbonyl compounds react differently is conjugation. There we introduced you to the idea that bringing two π systems (two C=C bonds, for example, or a C=C bond and a C=O bond) close together leads to a stabilizing interaction. It also leads to modified reactivity, because the π bonds no longer react as independent functional groups but as a single, conjugated system.

●Conjugation makes alkenes electrophilic

• C=C double bonds are nucleophilic

• C=C double bonds conjugated with carbonyl groups can be electrophilic

مواضيع ذات صلة

Reaction conditions

Alkenes conjugated with carbonyl groups

Two reasons to avoid a Friedel–Crafts alkylation

Two or more substituents may cooperate or compete

Phenols react rapidly with bromine

Alkyl and acyl substituents can be added to a benzene ring by the Friedel–Crafts reaction

Sulfonation of benzene

Nitration of benzene

Benzene and its reactions with electrophiles

enols and phenols

Reactions of silyl enol ethers with halogen and sulfur electrophiles

Reactions of enol ethers Hydrolysis of enol ethers