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A Levels Chemistry (9701)•9701/13/M/J/21
Question 28 from 9701/13/M/J/21

Explanation

Nitriles hydrolyze to carboxylic acids with acid or base

Steps:

  • Target product is 2-methylbutanoic acid: CH3CH2CH(CH3)COOH.
  • Nitriles undergo hydrolysis (R-CN → RCOOH) with single reagent like H3O+ or OH-/H+.
  • 2-Methylbutanenitrile is NC-CH(CH3)CH2CH3, so R = CH(CH3)CH2CH3 matches the acid's chain.
  • Other options lack this direct conversion or produce wrong products.

Why C is correct:

  • Hydrolysis converts the -CN group of 2-methylbutanenitrile to -COOH, yielding exactly 2-methylbutanoic acid.

Why the others are wrong:

  • A: Pentan-2-one is a ketone that does not hydrolyze or oxidize to a carboxylic acid with one reagent.
  • B: 2-Methylbutan-2-ol is a tertiary alcohol that resists oxidation to carboxylic acids.
  • D: 2-Methylpropanenitrile hydrolyzes to 2-methylpropanoic acid, which has a shorter carbon chain.

Final answer: C

Topic: Nitrogen compounds

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