Question

Explain the mechanism of nucleophilic addition reaction in aldehydes and ketones by an example. Write chemical equations of the reaction of Aldol and Cross Aldol condensation.

Hint:

Nucleophilic addition occurs due to the electrophilic nature of the carbonyl carbon.

Answer 1

Mechanism of Nucleophilic Addition Reaction: Aldehydes and ketones undergo nucleophilic addition reactions due to the presence of a polar carbonyl group (\( C=O \)).  

Step 1: Nucleophilic attack on the carbonyl carbon: \[ R-C(=O)-R' + Nu^- \rightarrow R-C(O^-)-R'Nu. \] 

Step 2: Protonation: \[ R-C(O^-)-R'Nu + H^+ \rightarrow R-C(OH)-R'Nu. \] 

Example: Reaction of formaldehyde with cyanide ion: \[ HCHO + CN^- \rightarrow H-C(CN)(OH). \]