Chapter 22.18, Problem 22.55P

Interpretation Introduction

Interpretation:

A mechanism for the conjugate addition of a nucleophile to acrylonitrile and to nitroethylene has to be proposed with the help of resonance forms.

Concept introduction:

Standard nucleophilic addition to a carbonyl group is $1,2$-addition. In the first step, nucleophile adds to carbonyl group to give alkoxide. Then, protonation of alkoxide takes place. $1,4$-addition is Michael addition. The nucleophile adds to beta carbon of $\alpha ,\beta$-unsaturated system to give enolate ion followed by protonation at oxygen to give an enol or on carbon to give a keto form.