Question

Identify the compound produced by the reduction of Ethanenitrile with Lithium aluminium hydride :

• A. Ethylamine
• B. Ethanal
• C. Propylamine
• D. Methylamine

Hint:

Always count the total number of carbon atoms in the nitrile (including the carbon in the CN group) to determine the name of the resulting amine.

Answer 1

The Correct Option is A

Step 1: Writing out the starting nitrile.
Ethanenitrile has the name root 'ethane', telling us there are two carbons in the chain, so its structure is $CH_3-C\equiv N$.
Step 2: What $LiAlH_4$ does to a nitrile.
Lithium aluminium hydride is a strong hydride donor and it adds hydrogen right across the carbon-nitrogen triple bond, four hydrogen atoms in total, turning that triple bond into a single bond with an $-NH_2$ group sitting on the terminal carbon. \[ CH_3-C\equiv N + 4[H] \xrightarrow{LiAlH_4} CH_3-CH_2-NH_2 \]
Step 3: Checking the carbon count carries over.
This reduction never breaks a carbon-carbon bond, so the product keeps exactly the same two carbons the nitrile started with. That rules out methylamine, which has only one carbon, and propylamine, which has three.
Step 4: Naming the product.
$CH_3CH_2NH_2$ is an ethyl group carrying an amino group, which is simply ethylamine. \[ \boxed{\text{Ethylamine}} \]