APSC ILM 2025: Wurtz reaction Paper 2

Which of the following alkanes cannot be prepared by Wurtz reaction?
(A) Methane
(B) Ethane
(C) Propane
(D) 2-Methylpropane

(A) Methane:

• Would require coupling of methyl halide (CH₃–X) with itself.
• This gives ethane (CH₃–CH₃), not methane.
• So methane cannot be prepared by Wurtz reaction.

(B) Ethane:

• Formed by coupling of two methyl halide molecules (CH₃–X).
• Ethane can be prepared.

(C) Propane:

• Would require coupling of methyl halide (CH₃–X) and ethyl halide (C₂H₅–X).
• This is unsymmetrical, and Wurtz reaction gives a mixture (ethane, propane, butane).
• Propane cannot be prepared cleanly.

(D) 2-Methylpropane (isobutane):

• Can be obtained by coupling of isopropyl halide (CH₃–CHBr–CH₃) and methyl halide.
• Again, leads to mixtures — not ideal.
• Cannot be prepared selectively.

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Final Correct Answer:

(A) Methane — it cannot be prepared by the Wurtz reaction.