Reaction of a carbonyl compound with one of the following reagents involves nucleophilic addition followed by

Question

Reaction of a carbonyl compound with one of the following reagents involves nucleophilic addition followed by the elimination of water. The reagent is:

Accepted Answer

The reaction of aldehydes and ketones with ammonia derivatives ($H_2N-Z$) is a characteristic **nucleophilic addition-elimination** reaction.

1.  **Mechanism:** The nitrogen atom of the nucleophile attacks the carbonyl carbon (nucleophilic addition) to form a tetrahedral intermediate. This intermediate then loses a molecule of water (elimination) to form a compound with a $>C=N-Z$ double bond.
2.  **Hydrazine:** Hydrazine ($NH_2NH_2$) reacts with carbonyl compounds in a feebly acidic medium to eliminate water and form **hydrazones**.
    $$ >C=O + H_2N-NH_2 \xrightarrow{H^+} >C=N-NH_2 + H_2O $$
3.  **Other Options:**
    *   **Grignard reagent:** Undergoes nucleophilic addition to form an alkoxide, which yields an alcohol upon hydrolysis (no water elimination in the addition step).
    *   **Hydrocyanic acid (HCN):** Undergoes nucleophilic addition to form cyanohydrins (no water elimination).
    *   **Sodium hydrogen sulphite:** Undergoes nucleophilic addition to form bisulphite addition products (no water elimination).

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