Given $p K_{a}$ values: phenol 10.0, 4-methylphenol 10.3, 3-nitrophenol 8.4, 4-nitrophenol 7.2. The decreasing order of acidity is

A4-nitrophenol $>$ phenol $>$ 3-nitrophenol $>$ 4-methylphenol
B4-methylphenol $>$ phenol $>$ 3-nitrophenol $>$ 4-nitrophenol
C4-nitrophenol $>$ 3-nitrophenol $>$ phenol $>$ 4-methylphenol
D3-nitrophenol $>$ 4-nitrophenol $>$ phenol $>$ 4-methylphenol

Answer: C

A smaller

p K_{a}

means a stronger acid. Ranking the given values:

7.2 < 8.4 < 10.0 < 10.3

, which gives 4-nitrophenol > 3-nitrophenol > phenol > 4-methylphenol. The para nitro group acts by resonance and induction, the meta one by induction only, and the methyl group destabilises the phenoxide.

Practice Alcohols, Phenols and Ethers More on Phenols: acidity, Kolbe, Reimer-Tiemann, electrophilic substitution

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Given pKa​ values: phenol 10.0, 4-methylphenol 10.3, 3-nitrophenol 8.4, 4-nitrophenol 7.2. The decreasing order of acidity is

Answer: C

More questions on Phenols: acidity, Kolbe, Reimer-Tiemann, electrophilic substitution

Given $p K_{a}$ values: phenol 10.0, 4-methylphenol 10.3, 3-nitrophenol 8.4, 4-nitrophenol 7.2. The decreasing order of acidity is