Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYEasy

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

2,3-Dimethylbutane

n-Heptane

n-Butane

n-Hexane

Principle of Wurtz Reaction: The Wurtz reaction involves the coupling of two alkyl halide molecules with sodium metal in dry ether to form higher alkanes ( $2RX + 2Na \rightarrow R-R + 2NaX$ ). This method is suitable for preparing symmetrical alkanes containing an even number of carbon atoms .
Analysis of Options:

n-Butane ( $C_4H_{10}$ ): Even number of carbons (4). Symmetrical ( $C_2H_5-C_2H_5$ ). Can be prepared from bromoethane.
n-Hexane ( $C_6H_{14}$ ): Even number of carbons (6). Symmetrical ( $C_3H_7-C_3H_7$ ). Can be prepared from 1-chloropropane.
2,3-Dimethylbutane ( $C_6H_{14}$ ): Even number of carbons (6). Symmetrical dimer of isopropyl chloride. Can be prepared effectively.
n-Heptane ( $C_7H_{16}$ ): Odd number of carbons (7). It is unsymmetrical. To prepare it, one would need two different alkyl halides (e.g., propyl halide and butyl halide). This results in a mixture of three products (propane, octane, and heptane) due to self-coupling and cross-coupling, making separation difficult and the yield of n-heptane poor .

Conclusion: Alkanes with an odd number of carbon atoms, like n-Heptane, cannot be prepared in good yield using the Wurtz reaction.

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