Which of the following nitriles gives butan-1-amine, CH3CH2CH2CH2NH2, on catalytic hydrogenation?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Butanenitrile, CH3CH2CH2CN
Nitriles are reduced to primary amines by catalytic hydrogenation (or by LiAlH4).
The carbon of the –C≡N group becomes the –CH2– next to nitrogen, so the amine keeps all the carbon atoms of the nitrile and its chain is not branched or shortened.
\( \displaystyle \ce{CH3CH2CH2C#N + 2H2} \xrightarrow{\ce{Ni}} \ce{CH3CH2CH2CH2NH2} \)
Butan-1-amine has four carbon atoms in a straight chain, so the nitrile must be the straight-chain C4 nitrile, butanenitrile (its name already counts the C of –CN).
Why the other options are incorrect
Option (1) Propanenitrile — Incorrect.
It has three carbon atoms and gives propan-1-amine, \( \ce{CH3CH2CH2NH2} \).
The amine keeps the carbon count of the nitrile; the “one carbon atom more” of this method is counted against the starting amine, not against the nitrile.
Option (3) Pentanenitrile — Incorrect. It has five carbon atoms and gives pentan-1-amine.
Option (4) 2-Methylpropanenitrile — Incorrect. It has four carbon atoms but a branched chain, so it gives 2-methylpropan-1-amine, \( \ce{(CH3)2CHCH2NH2} \).
NCERT (2026-27 edition):
9.4 Preparation of Amines – “3. Reduction of nitriles: Nitriles on reduction with lithium aluminium hydride (LiAlH4) or catalytic hydrogenation produce primary amines. This reaction is used for ascent of amine series, i.e., for preparation of amines containing one carbon atom more than the starting amine.”