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Question
Among the following compounds, the most acidic is :
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Solution
The correct option is C o-hydroxybenzene acid
A monosubstituted benzoic acid is stronger than a monosubstituted phenol as former being a carboxylic acid. Among the given substituted benzoic acid, o-hydroxybenzene acid is the strongest acid although -OH causes electron donation by resonance effect which tends to decrease acid strength.
It is due to a very high stabilization of conjugate base by intramolecular H-bond which outweigh the electron-donating resonance effect of -OH.
The overall order of acid strength of given four acids is :o-hydroxybenzene acid (pKa = 2.98 )> p-toluic acid (pKa = 4.37)>p-hydrobenzoic acid(pKa = 4.58)>p-nitrophenol(pKa = 7.15)
Hence the correct option is 'C'.
A monosubstituted benzoic acid is stronger than a monosubstituted phenol as former being a carboxylic acid.
Among the given substituted benzoic acid, o-hydroxybenzene acid is the strongest acid although -OH causes electron donation by resonance effect which tends to decrease acid strength.
It is due to a very high stabilization of conjugate base by intramolecular H-bond which outweigh the electron-donating resonance effect of -OH.
The overall order of acid strength of given four acids is :
o-hydroxybenzene acid (pKa = 2.98 )> p-toluic acid (pKa = 4.37)>p-hydrobenzoic acid(pKa = 4.58)>p-nitrophenol(pKa = 7.15)
Hence the correct option is 'C'.
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