Which of the following compound cannot be prepared singly by the Wurtz reaction ?

Options

A. `C_2H_6`
B. `(CH_3)_2CHCH_2`
C. `CH_3CH_2CH_2CH_3`
D. All of the above can be prepared

Answer

To determine which compound cannot be prepared singly by the Wurtz reaction, we first need to understand the Wurtz reaction itself. The Wurtz reaction involves the coupling of alkyl halides in the presence of sodium metal and dry ether to form alkanes.

### Step-by-Step Solution:

1. **Understanding the Wurtz Reaction**:
- The Wurtz reaction is a method to synthesize alkanes by coupling two alkyl halides using sodium metal (Na) in dry ether.
- The general reaction can be represented as:
\[ 2 R-X + 2 Na \xrightarrow{\text{dry ether}} R-R + 2 NaX \]
- Here, R represents the alkyl group and X represents the halogen.

2. **Analyzing the Compounds**:
- We need to analyze the compounds provided in the question to see if they can be formed through the Wurtz reaction.
- The compounds typically considered are:
1. Ethane (C2H6)
2. Butane (C4H10)
3. Propane (C3H8)
4. A compound that cannot be formed by the Wurtz reaction.

3. **Forming Alkanes**:
- **Ethane** can be formed from two molecules of methyl chloride (CH3Cl):
\[ 2 \text{CH}_3\text{Cl} + 2 \text{Na} \rightarrow \text{C}_2\text{H}_6 + 2 \text{NaCl} \]
- **Butane** can be formed from two molecules of ethyl bromide (C2H5Br):
\[ 2 \text{C}_2\text{H}_5\text{Br} + 2 \text{Na} \rightarrow \text{C}_4\text{H}_{10} + 2 \text{NaBr} \]
- **Propane**, however, cannot be formed from a single type of alkyl halide using the Wurtz reaction.

4. **Conclusion**:
- Among the compounds listed, **propane (C3H8)** cannot be prepared singly by the Wurtz reaction because it requires a specific combination of alkyl groups that cannot be achieved through the coupling of identical alkyl halides.

### Final Answer:
**Propane (C3H8) cannot be prepared singly by the Wurtz reaction.**