Compund (A), `C_(5)H_(11)NO` is not soluble in cold alkaline or acidic solutions. When (A) is refluxed in NaOH solution, a gas (B) is evolved and salt (C) is formed. Acetyl chloride reacts with (B) to give (D), `(C_(4)H_(9)NO)`. (B) reacts with `HNO_(2)` to give a yellow oil (E). Give structures of (A) to (E) with reason.

Answer

To solve the problem step by step, we will identify the structures of compounds A to E based on the information given in the question.

### Step 1: Identify Compound A
We know that compound A has the molecular formula `C5H11NO` and is not soluble in cold alkaline or acidic solutions. This suggests that it is likely a substituted amide.

Given the formula, a reasonable structure for compound A could be:
- **Structure of A**: `CH3-CH2-CH2-C(=O)-N(CH3)2` (This is N,N-dimethylpropenamide).

### Step 2: Reaction of Compound A with NaOH
When compound A is refluxed with NaOH, it undergoes hydrolysis, forming a gas (B) and a salt (C). The gas evolved is likely to be ammonia (NH3) due to the breakdown of the amide.

- **Gas B**: `NH3` (Ammonia)
- **Salt C**: The salt formed from the hydrolysis is sodium propanoate, which can be represented as `CH3-CH2-COO^- Na^+`.

### Step 3: Reaction of Gas B with Acetyl Chloride
Gas B (NH3) reacts with acetyl chloride (CH3COCl) to form compound D. The reaction involves the formation of an amide.

- **Structure of D**: `CH3-CO-N(CH3)2` (This is N,N-dimethylacetamide).
- **Molecular formula of D**: `C4H9NO`.

### Step 4: Reaction of Gas B with HNO2
Gas B (NH3) reacts with nitrous acid (HNO2) to form a yellow oily liquid (E). The reaction of a primary or secondary amine with nitrous acid typically leads to the formation of a nitrosamine.

- **Structure of E**: `CH3-CH2-N(NO)-CH3` (This is N,N-dimethyl-N-nitrosoamide).
- This compound is a yellow oily liquid.

### Summary of Structures
1. **Compound A**: N,N-dimethylpropenamide (`CH3-CH2-CH2-C(=O)-N(CH3)2`)
2. **Gas B**: Ammonia (`NH3`)
3. **Salt C**: Sodium propanoate (`CH3-CH2-COO^- Na^+`)
4. **Compound D**: N,N-dimethylacetamide (`CH3-CO-N(CH3)2`)
5. **Compound E**: N,N-dimethyl-N-nitrosoamide (`CH3-CH2-N(NO)-CH3`)