Organic Chemistry Basics Result Question 21
21. Among the following compounds, the most acidic is
(a) $p$-nitrophenol
(b) $p$-hydroxybenzoic acid
(c) $o$-hydroxybenzoic acid
(d) $p$-toluic acid
(2011)
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Answer:
Correct Answer: 21. ( c )
Solution:
- A mono-substituted benzoic acid is stronger than a mono-substituted phenol as former being a carboxylic acid. Among the given substituted benzoic acid, ortho-hydroxy acid is strongest acid although $-\mathrm{OH}$ causes electron donation by resonance effect which tends to decrease acid strength.
It is due to a very high stabilisation of conjugate base by intramolecular $\mathrm{H}$-bond which outweigh the electron donating resonance effect of $-\mathrm{OH}$.
BETA
