Which of the following alkanes is not obtained by Wurtz reaction ?

Options

A. Methane
B. Ethane
C. butane
D. hexane

Answer

To determine which alkane is not obtained by the Wurtz reaction, we need to understand the mechanism of the Wurtz reaction and analyze the given options: methane, ethane, butane, and hexane.

### Step-by-Step Solution:

1. **Understanding the Wurtz Reaction**:
- The Wurtz reaction involves the coupling of two alkyl halides in the presence of sodium (Na) and dry ether. The general reaction can be represented as:
\[ 2 R-X + 2 Na \rightarrow R-R + 2 NaX \]
- Here, \( R \) is the alkyl group and \( X \) is a halogen (like Cl, Br, or I).

2. **Identifying the Alkyl Halides**:
- For the Wurtz reaction to occur, each alkyl halide must have at least one carbon atom. Therefore, the minimum number of carbon atoms in the resulting alkane must be 2 (since we are combining two alkyl groups).

3. **Analyzing the Given Options**:
- **Methane (CH₄)**: This alkane has only one carbon atom. Since we need at least two alkyl groups to perform the Wurtz reaction, methane cannot be formed through this method.
- **Ethane (C₂H₆)**: This can be formed by coupling two methyl halides (e.g., CH₃Br).
- **Butane (C₄H₁₀)**: This can be formed by coupling two ethyl halides (e.g., C₂H₅Br).
- **Hexane (C₆H₁₄)**: This can be formed by coupling two propyl halides (e.g., C₃H₇Br).

4. **Conclusion**:
- Since methane is the only alkane listed that cannot be obtained from the Wurtz reaction (as it requires at least two carbon atoms), the answer is:
\[ \text{Methane (CH₄)} \]

### Final Answer:
**Methane (CH₄)** is the alkane that is not obtained by the Wurtz reaction.

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