Question

Which from the following compounds is not obtained when methyl bromide is treated with ethyl bromide in presence of sodium metal in dry ether?

• A. n-Butane
• B. Ethane
• C. Propane
• D. 2-methyl propane

Hint:

Cross Wurtz coupling gives three alkanes: propane, ethane, n-butane.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
In the Wurtz reaction two alkyl groups join. With two different halides, three couplings are possible.

Step 2: Possible Couplings:
\(\text{CH}_3 + \text{CH}_3\) gives ethane.
\(\text{CH}_3 + \text{C}_2\text{H}_5\) gives propane.
\(\text{C}_2\text{H}_5 + \text{C}_2\text{H}_5\) gives n-butane.

Step 3: Check Option (D):
2-methylpropane, \(\text{CH}_3\text{CH}(\text{CH}_3)_2\), has a branched carbon skeleton. Joining methyl and ethyl groups can never create a branch, so it cannot be formed.

Step 4: Conclusion:
Ethane, propane and n-butane are all products. 2-methylpropane is not, so (D) is the answer.

Final Answer:
2-methylpropane cannot form, option (D). \[ \boxed{\text{(D) 2-methylpropane}} \]