acidity order

Question

Which is the correct acidity order (strongest acid first)?

RankGuru · Accepted Answer

1. **Substituent Effects on Acidity**:
   - **Electron Withdrawing Groups (EWG)** like $-NO_2$ stabilize the phenoxide ion, **increasing** acidity.
   - **Electron Donating Groups (EDG)** like $-CH_3$ destabilize the phenoxide ion, **decreasing** acidity.
2. **Analysis**:
   - **p-Nitrophenol**: Has a strong EWG ($-NO_2$). Most acidic.
   - **Phenol**: No substituents. Baseline acidity.
   - **p-Cresol**: Has a methyl group (EDG, $+I$ and hyperconjugation). Least acidic.
3. **Result**: **p-nitrophenol > phenol > p-cresol**.

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acidity order

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