An alkyl bromide (X) reacts with Na to form 4,5-diethyloctane. Compound X is:

Options

A. `CH_(3)(CH_(2))_(3)`Br
B. `CH_(3)(CH_(2))_(5)`Br
C. `CH_(3)(CH_(2))_(3)`CH.Br.`CH_(3)`
D. `CH_(3)(CH_(2))_(2)`CH.Br.`CH_(2)CH_(3)`

Answer

To determine the alkyl bromide (X) that reacts with sodium to form 4,5-diethyloctane, we can follow these steps:

### Step 1: Understand the Product Structure
The product given is 4,5-diethyloctane. This indicates that the compound has an octane backbone (8 carbon atoms) with ethyl groups attached to the 4th and 5th carbon atoms.

### Step 2: Write the Structure of 4,5-Diethyloctane
The structure of 4,5-diethyloctane can be represented as:
```
CH2CH3
|
CH3-CH2-CH2-CH-CH-CH2-CH3
|
CH2CH3
```
This shows that the main chain consists of 8 carbon atoms, with two ethyl groups on the 4th and 5th positions.

### Step 3: Identify the Reaction Type
The reaction described is a Wurtz reaction, where two equivalents of an alkyl halide react with sodium to form an alkane. This means that the alkyl bromide (X) must have a structure that can yield 4,5-diethyloctane when reacted with sodium.

### Step 4: Determine the Alkyl Bromide Structure
Since the Wurtz reaction doubles the number of carbon atoms, we need to find an alkyl bromide that has half the number of carbon atoms in the final product. Therefore, we need an alkyl bromide that has 4 carbon atoms (since 4 carbon atoms from two equivalents will yield 8 carbon atoms in the product).

### Step 5: Analyze the Options
We will analyze the given options for alkyl bromides to see which one can yield 4,5-diethyloctane:

1. **Option 1: CH3CH2CH2CH2Br (1-bromobutane)**
- Reaction with sodium would yield CH3CH2CH2CH2-CH3 (butane), which is incorrect.

2. **Option 2: CH3(CH2)6Br (1-bromohexane)**
- Reaction with sodium would yield CH3(CH2)10CH3 (dodecane), which is incorrect.

3. **Option 3: CH3CH2CH2CHBrCH2CH3 (2-bromohexane)**
- Reaction with sodium would yield CH3CH2CH2CH(CH2CH3)CH(CH2CH3)CH2CH3, which does not yield 4,5-diethyloctane.

4. **Option 4: CH3CH2CHBrCH2CH2CH3 (3-bromohexane)**
- Reaction with sodium would yield CH3CH2CH(CH2CH3)CH(CH2CH3)CH2CH3, which gives the desired product 4,5-diethyloctane.

### Conclusion
The correct alkyl bromide (X) that reacts with sodium to form 4,5-diethyloctane is **CH3CH2CHBrCH2CH2CH3** (3-bromohexane).