Q6 / 180 · KCET 2014 · Chemistry

The acid strength of active methylene group in
(a) \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOC}_{2} \mathrm{H}_{5} \)
(b) \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COCH}_{3} \)
(c) \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OOCCH}_{2} \mathrm{COOC}_{2} \mathrm{H}_{5} \)
decreases as

  • A
    \( a>b>0 \)
  • B
    c> a> b
  • C
    \( a>c>b \)
  • Correct answer
    D
    \( b>a>c \)

Solution

An active methylene compound is a compound that has the following general structural formula.
Figure
Where, \( E_{1} \) and \( E_{2} \) are functional group that withdraws electron by resonance. After the removal of hydrogen from the
active methylene groups, the carbanion thus, formed is stabilized by the resonance. Greater the stabilization of the
carbanion, greater will be the acidic strength of the active methylene groups.
(।) \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COOC}_{2} \mathrm{H}_{5} \)
Figure
So, ketonic groups stabilized more carbanion ion than the ester or carboxylic groups. Therefore, compound having more
number of ketonic groups is more acidic active methylene compound.
(II) \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{COCH}_{3} \)
Figure
(III) \( \mathrm{CH}_{3} \mathrm{COOCH}_{2} \mathrm{COOCH}_{3} \)
Figure

Hence, the correct answer is option: 'D'.

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