The simplest conjugated nitrile is acrylonitrile. This compound adds amines readily. No special conditions are needed to encourage attack at C=C rather than C≡N because the nitrile carbon is rather unreactive as an electrophilic centre.

The amine first attacks the alkene in a typical conjugate addition to make an anion stabilized by being next to the nitrile. The anion can have its charge drawn on C or N: it is delocalized like an enolate. Do not be put off by the odd appearance of the ‘enolate’. The dot between the two double bonds is a reminder that there is a linear spcarbon atom at this point.

Protonation at carbon restores the nitrile and gives the product—an amino-nitrile. The whole process adds a 2-cyano-ethyl group to the amine and is known industrially as cyanoethylation.

Protonation at carbon restores the nitrile and gives the product—an amino-nitrile. The whole process adds a 2-cyano-ethyl group to the amine and is known industrially as cyanoethylation.

With a primary amine, the reaction need not stop at that stage as the product is still nucleophilic and a second addition can occur to replace the second hydrogen atom on nitrogen.

Other elements such as O, S, or P can add too. Phenyl phosphine can undergo a double addition just as in the last example, but alcohols can add only once. If there is competition between a fi rst-row (for example N or O) and a second-row (for example S or P) element, the second-row element normally wins

The nitro group (NO₂) is extremely electron-withdrawing—about twice as electron-with drawing as a carbonyl group. It is also unreactive as an electrophilic centre, which makes conjugate addition to nitro-alkenes a very reliable reaction. In this example, sodium boro hydride attacks the C=C bond in a conjugate manner to give an intermediate looking rather like an enolate anion, with a negatively charged oxygen atom conjugated to an (N=C) double bond. It reacts like an enolate too, picking up a proton on carbon to re-form the nitro group and give a stable product.

مواضيع ذات صلة

How to reduce carboxylic acids to alcohols

How to reduce amides to amines

The benzyne mechanism

Other nucleophiles

The SN1 mechanism for nucleophilic aromatic substitution: diazonium compounds

The activating anion-stabilizing substituent

The leaving group and the mechanism

The intermediate in the addition–elimination mechanism

The addition–elimination mechanism

Nucleophilic aromatic substitution

Nucleophilic epoxidation

Conjugate substitution reactions