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NCERT Class XII Chemistry
Chapter - Alcohols, Phenols and Ethers
Questions with Solutions

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Question : 27
Total: 45
Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.
Solution:  
Consider the reaction between propan-2-ol molecules in the presence of acid.
CH3−
CH3
|
C
H−OH
H+
––––––––▶
CH3−
CH3
|
C
⊕
H
If an ether is to be formed, another alcohol molecule must carry out a nucleophilic attack on the carbocation as
However, this does not happen because of
(a) the steric hindrance around the carbocation, and (b) bulky size of the nucleophile which would further cause crowding.
As a result, the carbocation prefers to lose a proton and forms an alkene.
For the same reason 3° alcohols in the presence of acid do not form etherssince 3° alcohols are even more sterically hindered than 2° alcohols.
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