What is the final product of following reactions ?
`Hex-3-"ynal" underset((i) PBr_3 , (ii) Mg//"ether",(iii) CO_2//H_3O^(+))overset((i) NaBH_4)to`

Options

A.
B.
C.
D.

Answer

To solve the given problem, we will go through the reactions step by step, starting from Hex-3-ynal and identifying the final product after each reaction.

### Step 1: Structure of Hex-3-ynal
Hex-3-ynal is an aldehyde with a triple bond at the 3rd carbon. The structure can be represented as follows:

```
CH3-CH2-C≡C-CHO
```

### Step 2: Reaction with NaBH4
NaBH4 is a reducing agent that will reduce the aldehyde group (-CHO) to a primary alcohol (-CH2OH). The product after this reaction (let's call it X) will be:

```
CH3-CH2-C≡C-CH2OH
```

### Step 3: Reaction with PBr3
Next, we treat the alcohol with PBr3, which will replace the -OH group with a bromine atom. The product after this reaction (let's call it Y) will be:

```
CH3-CH2-C≡C-CH2Br
```

### Step 4: Reaction with Mg in Ether
The next step involves treating the alkyl bromide (Y) with magnesium in dry ether to form a Grignard reagent (let's call it Z). The structure of the Grignard reagent will be:

```
CH3-CH2-C≡C-CH2-MgBr
```

### Step 5: Reaction with CO2
The Grignard reagent will then react with carbon dioxide (CO2). The carbon atom of the Grignard reagent will attack the carbon of CO2, resulting in the formation of a carboxylate intermediate. The structure at this stage (let's call it P) will be:

```
CH3-CH2-C≡C-CH2-COO^-
```

### Step 6: Hydrolysis
Finally, we perform hydrolysis of the carboxylate intermediate using H3O+. This will convert the carboxylate (-COO^-) into a carboxylic acid (-COOH). The final product will be:

```
CH3-CH2-C≡C-CH2-COOH
```

### Final Product
The final product after all the reactions is:

```
CH3-CH2-C≡C-CH2-COOH
```

This compound has 7 carbon atoms and a carboxylic acid functional group.

### Summary of Steps:
1. **Hex-3-ynal** → Reduction with NaBH4 → **Hex-3-ynol** (X)
2. **Hex-3-ynol** → Reaction with PBr3 → **Hex-3-ynyl bromide** (Y)
3. **Hex-3-ynyl bromide** → Reaction with Mg in ether → **Grignard reagent** (Z)
4. **Grignard reagent** → Reaction with CO2 → **Carboxylate intermediate** (P)
5. **Carboxylate** → Hydrolysis with H3O+ → **Final product: Hex-3-ynoic acid**