Question

Which of the following alkane cannot be made in good yield by Wurtz reaction ?

• A. n-Hexane
• B. 2,3-Dimethylbutane
• C. n-Heptane
• D. n-Butane

Answer 1

The Correct Option is C

The Wurtz reaction is a coupling reaction in organic chemistry, used to synthesize symmetrical alkanes by the reaction of two alkyl halides with sodium metal in dry ether. The general reaction can be represented as follows:

\(\text{2 R-X} + \text{2Na} \rightarrow \text{R-R} + \text{2NaX}\)

where \(\text{R}\) is the alkyl group and \(\text{X}\) is the halide.

The Wurtz reaction works well for synthesizing symmetrical alkanes but has limitations when attempting to create unsymmetrical alkanes due to possible side reactions and a mixture of products.

To determine which alkane listed cannot be synthesized in good yield by the Wurtz reaction, let's analyze each option:

1. n-Hexane: This is a symmetrical alkane and can be synthesized by using 1-bromobutane or 1-chlorobutane as the alkyl halide. For example, using two molecules of 1-bromobutane: \(2 \text{CH}_3\text{(CH}_2)_3\text{Br} + 2 \text{Na} \rightarrow \text{CH}_3\text{(CH}_2)_4\text{CH}_3 + 2 \text{NaBr}\) Since \(\text{n-Hexane}\) is symmetrical, it can be synthesized in good yield.
2. 2,3-Dimethylbutane: An unsymmetrical alkane can still be synthesized with careful choice of alkyl halides, but it typically results in lower yield and a mixture of products.
3. n-Heptane: This is an unsymmetrical alkane that cannot be efficiently synthesized using the Wurtz reaction due to the difficulty in controlling the reaction to produce this specific unsymmetrical alkane without side reactions and mixture of products. Wurtz reaction works best for synthesizing symmetrical alkanes.
4. n-Butane: This is a symmetrical alkane and can be prepared using ethyl bromide: \(2 \text{C}_2\text{H}_5\text{Br} + 2 \text{Na} \rightarrow \text{C}_4\text{H}_{10} + 2 \text{NaBr}\) Because \(\text{n-Butane}\) is symmetrical, it can be synthesized in good yield.

Therefore, the correct answer is that n-Heptane cannot be made in good yield by the Wurtz reaction because it is an unsymmetrical alkane, and the Wurtz reaction tends to produce mixtures of products when unsymmetrical compounds are involved.