Question

Which statement correctly contrasts Clemmensen and Wolff-Kishner reductions?

• A. Clemmensen uses base, Wolff-Kishner uses acid
• B. Both are done under acidic conditions
• C. Clemmensen is for compounds stable in acid and uses Zn-Hg/HCl; Wolff-Kishner is for those stable in base and uses hydrazine/KOH
• D. Both only reduce carboxylic acids

Hint:

Clemmensen reduction is used under acidic conditions with Zn-Hg/HCl, while Wolff-Kishner is used under basic conditions with hydrazine/KOH.

Answer 1

The Correct Option is C

Step 1: Understanding the Clemmensen reduction.
The Clemmensen reduction is used to reduce carbonyl compounds (such as aldehydes or ketones) to alkanes. It is performed under acidic conditions using zinc amalgam (Zn-Hg) and hydrochloric acid (HCl). This method is suitable for compounds that are stable in acidic conditions.
Step 2: Understanding the Wolff-Kishner reduction.
The Wolff-Kishner reduction is also used to reduce carbonyl compounds, but it requires basic conditions. It uses hydrazine (N2H4) and potassium hydroxide (KOH) under heat. This method is more suitable for compounds that are stable in basic conditions.
Step 3: Conclusion.
The correct statement is (C), which contrasts the two reductions based on their required conditions: Clemmensen uses Zn-Hg/HCl under acidic conditions, while Wolff-Kishner uses hydrazine/KOH under basic conditions.

Answer 2

Step 1: Clemmensen reduction reduces carbonyl (C=O) compounds to alkanes, and needs acidic conditions — zinc amalgam (Zn-Hg) with HCl. It suits compounds stable in acid.

Step 2: Wolff-Kishner reduction does the same job under basic conditions — hydrazine with KOH and heat. It suits compounds stable in base.

Step 3: So the correct contrast is: Clemmensen = acid-stable compounds with Zn-Hg/HCl; Wolff-Kishner = base-stable compounds with hydrazine/KOH — option (C).

Answer 3

Elimination approach: Saying Clemmensen uses base and Wolff-Kishner uses acid reverses the actual conditions, so that's wrong. Saying both use acid is wrong too, since Wolff-Kishner specifically needs a basic medium of hydrazine and KOH. Saying both only reduce carboxylic acids is wrong because both act on carbonyl compounds like aldehydes and ketones, not carboxylic acids. What's left correctly states Clemmensen works on acid-stable substrates with zinc amalgam and HCl, while Wolff-Kishner works on base-stable substrates with hydrazine and KOH, option (C).