`CH_(3)CN overset(CH_(3)MgBr(2" mol"))underset(H_(3)O^(+))to A overset("conc. "H_(2)SO_(4))to B`
A and B are

Options

A.
B. `(CH_(3))_(3)COH,(CH_(3))_(2)C=CH_(2)`
C. `(CH_(3))_(2)CHOH,CH_(3)CH=CH_(2)`
D. None is correct

Answer

To solve the problem, we will follow the steps outlined in the video transcript and break down the reactions step by step.

### Step 1: Reaction of CH₃CN with CH₃MgBr
1. **Starting Material**: We have CH₃CN (acetonitrile), which contains a carbon atom triple-bonded to a nitrogen atom.
2. **Nucleophilic Attack**: The Grignard reagent CH₃MgBr acts as a nucleophile. The carbon atom in the nitrile (C≡N) is electrophilic due to the electronegative nitrogen atom pulling electron density away from it.
3. **Formation of an Intermediate**: The nucleophilic CH₃ group from CH₃MgBr attacks the electrophilic carbon of the nitrile, resulting in the formation of an intermediate:
\[ CH₃C(=N)MgBr \]
This intermediate has a carbon double-bonded to nitrogen and a magnesium bromide group attached.

### Step 2: Hydrolysis of the Intermediate
1. **Hydrolysis**: When we add H₃O⁺ (acidic hydrolysis), the intermediate undergoes hydrolysis. The nitrogen atom will attract a hydrogen ion from water, leading to the formation of an amine and a carbonyl compound:
\[ CH₃C(=O)CH₃ + NH₄^+ + MgBr^- \]
Here, we have formed an amide (CH₃C(=O)NH₂) and a byproduct of ammonium ion and magnesium bromide.

### Step 3: Conversion of A to B using Concentrated H₂SO₄
1. **Formation of B**: The amide (A) can be treated with concentrated sulfuric acid (H₂SO₄), which will lead to dehydration and the formation of an imine or an amide derivative:
\[ CH₃C(=O)NH₂ \overset{H₂SO₄}{\rightarrow} CH₃C(=O) + H₂O \]
This step results in the formation of a ketone (B).

### Final Products
- **A**: The product after the first reaction and hydrolysis is **Acetamide (CH₃C(=O)NH₂)**.
- **B**: The product after dehydration using concentrated sulfuric acid is **Acetone (CH₃C(=O)CH₃)**.

### Summary
- **A**: Acetamide (CH₃C(=O)NH₂)
- **B**: Acetone (CH₃C(=O)CH₃)