Question:
The correct order of acidity of the following compounds is
The correct order of acidity of the following compounds is
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Electron-donating groups decrease acidity of phenols, while electron-withdrawing groups increase acidity.
Updated On: Jun 15, 2026
- \(III\gt II\gt I\)
- \(II\gt III\gt I\)
- \(I\gt II\gt III\)
- \(III\gt I\gt II\)
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The Correct Option is C
Solution and Explanation
Step 1: Recall the effect of substituents on acidity.
Acidity of phenols depends on the stability of the phenoxide ion formed after loss of proton.
Electron-donating groups decrease acidity because they destabilize the phenoxide ion.
Step 2: Analyze compound I.
Compound I is phenol. It has no electron-donating substituent, so it shows the highest acidity among the three compounds.
Step 3: Analyze compound II.
Compound II contains a methyl group \((\mathrm{-CH_3})\), which shows \(+I\) effect and donates electrons.
This decreases the stability of phenoxide ion and reduces acidity.
Thus,
\[ \text{Phenol} \gt p\text{-cresol} \]
Step 4: Analyze compound III.
Compound III contains a methoxy group \((\mathrm{-OCH_3})\), which strongly donates electrons by resonance effect \((+M)\).
This greatly destabilizes the phenoxide ion, making it the least acidic compound.
Therefore,
\[ p\text{-cresol} \gt p\text{-methoxy phenol} \]
Step 5: Write the final order.
Hence, the acidity order is
\[ I\gt II\gt III \]
Step 6: Final conclusion.
Therefore, the correct order of acidity is
\[ \boxed{I\gt II\gt III} \]
Acidity of phenols depends on the stability of the phenoxide ion formed after loss of proton.
Electron-donating groups decrease acidity because they destabilize the phenoxide ion.
Step 2: Analyze compound I.
Compound I is phenol. It has no electron-donating substituent, so it shows the highest acidity among the three compounds.
Step 3: Analyze compound II.
Compound II contains a methyl group \((\mathrm{-CH_3})\), which shows \(+I\) effect and donates electrons.
This decreases the stability of phenoxide ion and reduces acidity.
Thus,
\[ \text{Phenol} \gt p\text{-cresol} \]
Step 4: Analyze compound III.
Compound III contains a methoxy group \((\mathrm{-OCH_3})\), which strongly donates electrons by resonance effect \((+M)\).
This greatly destabilizes the phenoxide ion, making it the least acidic compound.
Therefore,
\[ p\text{-cresol} \gt p\text{-methoxy phenol} \]
Step 5: Write the final order.
Hence, the acidity order is
\[ I\gt II\gt III \]
Step 6: Final conclusion.
Therefore, the correct order of acidity is
\[ \boxed{I\gt II\gt III} \]
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