NCERT Class XII Chemistry
Chapter - Alcohols, Phenols and Ethers
Questions with Solutions
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Question : 33
Total: 45
When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place:
[Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.]
Give a mechanism for this reaction.
[Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.]
Solution:
The given reaction is an example of carbocation rearrangement which takes place by hydride shift. The mechanism for it is:
Step 1 : Formation of carbocation : Protonation of alcohol.
Step 3 : Attack of nucleophile : Generation of product
Step 1 : Formation of carbocation : Protonation of alcohol.
Step 2 : 1,2-hydride shift : Formation of a more stable, 3° carbocation.
Initially, a 2° carbocation (I) was formed. But, due to the higher stability of its 3° counter part, the hydride shift takes place and the more stable carbocation (II) is formed.
Step 3 : Attack of nucleophile : Generation of product
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