Ques. 1AIPMT 2007
In the reaction : CH3- CH3 |CH-CH2-O-CH2-CH3 + HI heated Which of the following compounds will be formed?
- CH3- CH3 |CH-CH3 + CH3CH2OH
- CH3- CH3 |CH-CH2OH + CH3CH3
- CH3- CH3 |CH-CH2OH + CH3CH2I
- CH3- CH3 |CH-CH2-I + CH3CH2OH
Answer
(3) CH3- CH3 |CH-CH2OH + CH3CH2I
Solution
As per NCERT, in the cleavage of a mixed ether (both groups primary/secondary) by HI, the oxygen is first protonated and then I- attacks the less hindered alkyl group by SN2 mechanism.
Here the two groups are isobutyl (–CH2CH(CH3)2, branched) and ethyl (–CH2CH3).
⇒ Ethyl is less hindered, so I- attacks the ethyl carbon:
CH3- CH3 |CH-CH2-O-CH2-CH3 + HI heated
CH3- CH3 |CH-CH2OH + CH3CH2I
∴ 2-Methylpropan-1-ol and iodoethane are formed.
Answer: (3)