Nucleophilic addition - Aldehydes and ketones

NUCLEOPHILIC ADDITION

Key Notes

Definition

Nucleophilic addition involves the addition of a nucleophile to an aldehyde or a ketone. The nucleophile adds to the electrophilic carbonyl carbon.

Overview

Charged nucleophiles undergo nucleophilic addition with an aldehyde or ketone to give a charged intermediate which has to be treated with acid to give the final product. Neutral nucleophiles require acid catalysis and fur- ther reactions can take place after nucleophilic addition.

Definition

As the name of the reaction suggests, nucleophilic addition involves the addition of a nucleophile to a molecule. This is a distinctive reaction for ketones and aldehydes and the nucleophile will add to the electrophilic carbon atom of the carbonyl group.  

The nucleophile can be a negatively charged ion such as cyanide or hydride, or it can be a neutral molecule such as water or alcohol.

Overview

In general, addition of charged nucleophiles results in the formation of a charged intermediate (Fig. 1). The reaction stops at this stage and acid has to be added tocomplete the reaction.

Neutral nucleophiles where nitrogen or oxygen is the nucleophilic center are relatively  weak  nucleophiles,  and  an  acid  catalyst  is  usually  required.  After nucleophilic addition has occurred, further reactions may take place leading to structures such as imines, enamines, acetals, and ketals.