Question

Which of the following is NOT obtained when a mixture of bromomethane and bromoethane is treated with sodium in dry ether?

• A. Propane
• B. Butane
• C. Methane
• D. Ethane

Hint:

The Wurtz reaction is strictly a coupling reaction that links two alkyl fragments together by forming a new carbon-carbon bond. Because it joins two carbon chains together, it is completely impossible to synthesize methane ($\text{CH}_4$), which contains only one single carbon atom, using this method.

Answer 1

The Correct Option is C

Step 1: Recognise the reaction.
Alkyl halides with sodium in dry ether is the Wurtz reaction, which couples alkyl groups by joining two radical fragments.
Step 2: List the radicals formed.
Bromomethane gives methyl radicals $\text{CH}_3^{\bullet}$ and bromoethane gives ethyl radicals $\text{C}_2\text{H}_5^{\bullet}$.
Step 3: Couple methyl with methyl.
$\text{CH}_3^{\bullet} + \text{CH}_3^{\bullet} \rightarrow \text{CH}_3\text{CH}_3$, giving ethane (2 carbons).
Step 4: Couple ethyl with ethyl.
$\text{C}_2\text{H}_5^{\bullet} + \text{C}_2\text{H}_5^{\bullet} \rightarrow \text{C}_4\text{H}_{10}$, giving butane (4 carbons).
Step 5: Couple methyl with ethyl.
$\text{CH}_3^{\bullet} + \text{C}_2\text{H}_5^{\bullet} \rightarrow \text{C}_3\text{H}_8$, giving propane (3 carbons).
Step 6: Check methane.
Every Wurtz product comes from joining two carbon fragments, so the smallest possible alkane has 2 carbons. Methane has only 1 carbon and cannot form by coupling.
Step 7: Conclude.
Ethane, butane and propane are all obtained, but methane is not.
\[ \boxed{\text{Methane is NOT obtained, option (3)}} \]