Question:

What is $ A $ in the following reaction?
\[ \mathrm{CH}_3-\mathrm{CH}= \mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CN} \xrightarrow{(1)\, \text{A} (\mathrm{i-Bu})_2} \xrightarrow{(2)\, \mathrm{H}_2\mathrm{O}} \rightarrow A \]

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Lithium aluminum hydride ($ LiAlH}_4 $) reduces nitriles to primary amines and does not affect double bonds unless specifically targeted.

Updated On: Jun 5, 2025

\[ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2 \]
\[ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2 \]
\[ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CHO} \]
\[ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CHO} \]

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The Correct Option is A

Solution and Explanation

Step 1: Analyze the Reaction.
The given reaction involves two steps:
1. Treatment with $ A(\mathrm{i-Bu})_2 $, where $ A $ is likely a reducing agent.
2. Subsequent treatment with water ($ \mathrm{H}_2\mathrm{O} $). The starting compound is:
\[ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CN} \] This is a conjugated alkene with a nitrile group ($ -\mathrm{CN} $) at the end.
Step 2: Identify the Reducing Agent.
The reagent $ A(\mathrm{i-Bu})_2 $ suggests that $ A $ is likely lithium aluminum hydride ($ \mathrm{LiAlH}_4 $), which is a strong reducing agent. Lithium aluminum hydride reduces:
- Alkenes to alkanes.
- Nitriles ($ -\mathrm{CN} $) to primary amines ($ -\mathrm{NH}_2 $).
Step 3: Apply the Reduction Steps.
1. Reduction of the Nitrile Group ($ -\mathrm{CN} $):
The nitrile group ($ -\mathrm{CN} $) is reduced to an amine ($ -\mathrm{NH}_2 $).
This step converts $ \mathrm{CN} $ to $ \mathrm{NH}_2 $. 2. Subsequent Treatment with Water:
After reduction, the product is treated with water. However, since the question only asks for the intermediate product after the first step, we focus on the reduction of the nitrile group.
Step 4: Determine the Structure of $ A $.
The starting compound is:
\[ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CN} \] After reduction of the nitrile group ($ -\mathrm{CN} $) to an amine ($ -\mathrm{NH}_2 $), the structure becomes:
\[ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2 \]
Step 5: Match with Options.
The options are:
1. $ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2 $
2. $ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2 $
3. $ \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CHO} $
4. $ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{CHO} $
The correct structure matches Option 1: \[ \boxed{\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{NH}_2} \]