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7. Alcohol, phenol and ethers — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistry7. Alcohol, phenol and ethers1 Mark
MCQ
The acidic hydrolysis of ether $( X )$ shown below is fastest when :
  • A
    one phenyl group is replaced by a methyl group.
  • B
    one phenyl group is replaced by a para-methoxyphenyl group.
  • ✓
    two phenyl groups are replaced by two para-methoxyphenyl groups.
  • D
    no structural change is made to $X$.
✓

Answer

Correct option: C.
two phenyl groups are replaced by two para-methoxyphenyl groups.
c
$Ph _3 C - CO \xrightarrow[ H _2 O ]{ H ^{\oplus}} Ph _3 C - OH + ROH$

The reaction proceeds by $S _{ N } 1$ Mechanism :

$Image$ 

Greater the electron releasing effect of the attached groups greater is the stability of intermediate carbocation, $\&$ faster is the rate of reaction

If two ph- groups are replaced by Me $Image$ groups, strong $+ M$ effect of $MeO -$ groups stablize, the carbocation better there by making the reaction faster.

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