A Levels Chemistry (9701)•9701/11/M/J/24
Explanation
LiAlH4 reduces carboxylic acids to primary alcohols Steps:
- Confirm P's formula C3H6O2 matches CH3CH2COOH in pair 1; pairs 2 and 3 have CH3COOH (C2H4O2), mismatch.
- Recall LiAlH4 with excess converts RCOOH to RCH2OH, retaining carbon count and yielding primary alcohol.
- Check pair 1: CH3CH2COOH (R=CH3CH2) → CH3CH2CH2OH, primary, C3H8O, matches.
- Check pairs 2 and 3: incorrect P formula; pair 3's Q is secondary alcohol, impossible from carboxylic acid.
Why A is correct:
- Pairs 1 and 2 show valid acid-to-primary alcohol reductions (pair 1 fits formula; pair 2 general case), per reduction mechanism.
Why the others are wrong:
- B includes pair 3's invalid secondary Q, violating primary alcohol rule.
- C excludes valid pair 1 and includes invalid pair 3.
Final answer: A
Topic: Carboxylic acids and derivatives
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