Question

Which of the following is NOT formed when a mixture of methyl bromide and n-propyl bromide is treated with sodium metal in dry ether?

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

Hint:

In Wurtz reaction with two different alkyl halides, the possible alkanes are: R–R, R'–R', and R–R'. To check if a given alkane can form, see if it can be written as a combination of the two alkyl groups present.

Answer 1

The Correct Option is B

Step 1: Understand the question.
Methyl bromide and n-propyl bromide are mixed with sodium in dry ether. This is the Wurtz reaction. We must find which alkane is NOT made.
Step 2: Recall the Wurtz reaction.
Sodium joins two alkyl groups together and removes the halogens. \[ 2R\text{-}X + 2Na \rightarrow R\text{-}R + 2NaX \]
Step 3: List the radical pieces.
The two pieces here are methyl ($CH_3$, 1 carbon) and n-propyl ($C_3H_7$, 3 carbons). With two different pieces, three pairings are possible.
Step 4: Pair them up.
Methyl plus methyl gives ethane (2 carbons). Propyl plus propyl gives hexane (6 carbons). Methyl plus propyl gives butane (4 carbons).
Step 5: Look for propane.
Propane has 3 carbons. To make it we would need a methyl piece plus an ethyl piece. But there is no ethyl bromide in the mix, so propane cannot form.
Step 6: Choose the answer.
The alkane not formed is propane, which is option 2. \[ \boxed{\text{Propane}} \]