Alcohols Phenols and Ethers - Result Question 43
####44. Correct increasing order of acidity is as follows:
[1994]
(a) $H_2 O, C_2 H_2, H_2 CO_3$, Phenol
(b) $C_2 H_2, H_2 O, H_2 CO_3$, Phenol
(c) Phenol, $C_2 H_2, H_2 CO_3, H_2 O$
(d) $C_2 H_2, H_2 O$, Phenol, $H_2 CO_3$
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Solution:
- (d) Such questions can be solved by considering the relative basic character of their conjugated bases which for $H_2 O, C_2 H_2, H_2 CO_3$ and $C_6 H_5 OH$ are
$ { }^{-} OH, HC=C^{-}, HCO_3^{-}, C_6 H_5 O^{-} $
More the possibility for the dispersal of the negative charge, weaker will be the base. Thus the relative basic character of the four bases is
$ HCO_3^{-}<C_6 H_5 O^{-}<-OH<HC=C^{-} $
Equivalent Non-equivalent Oxygen can accommodate
resonating structures $\quad(-)$ charge easily
Due to resonance
Thus, the acidic character of the four corresponding acids wil be
$ HC=CH<H_2 O<C_6 H_5 OH<H_2 CO_3 $
