Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 12

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Q: 25. Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example.

Answer

Wurtz reaction is limited for the synthesis of symmetrical alkanes (alkanes with an even number of carbon atoms) In the reaction, two similar alkyl halides are taken as reactants and an alkane, containing double the number of carbon atoms, are formed. Example:

Q 25 Ans 1 Structure of Wurtz Reaction is Limited for the Sy …

Q 25 Ans 1 Wurtz Reaction Limited for Alkanes

Wurtz reaction cannot be used for the preparation of unsymmetrical alkanes because if two dissimilar alkyl halides are taken as the reactants, then a mixture of alkanes is obtained as the products. Since the reaction involves free radical species, a side reaction also occurs to produce an alkene. For example, the reaction of bromoethane and iodoethane gives a mixture of alkanes.

Q 25 Ans 1 Structure of Reaction of Bromoethane and Iodoetha …

Reaction of Bromoethane and Iodoethane

The boiling points of alkanes (obtained in the mixture) are very close. Hence, it becomes difficult to separate them.

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