The correct order for acidity of the following hydroxyl compounds is:
Alcohols, Phenols & Ethers · Class 12 · JEE Main Previous Year Question
The correct order for acidity of the following hydroxyl compounds is:
- a✓
E > C > D > A > B
- b
D > E > C > A > B
- c
C > E > D > B > A
- d
E > D > C > B > A
E > C > D > A > B
Step 1: Assign approximate pKa values
| Compound | Type | pKa (approx) | |---|---|---| | (E) p-Nitrophenol | EWG (-NO2) at para | 7.1 | | (C) Phenol | No substituent | 10.0 | | (D) p-Methoxyphenol | EDG (-OMe) at para | 10.2 | | (A) Methanol | Aliphatic alcohol | 15.5 | | (B) tert-Butanol | Aliphatic, branched | 18.0 |
Step 2: Explain the trends
- (E) > (C): p-NO2 is EWG → stabilizes phenoxide via resonance → more acidic than phenol.
- (C) > (D): p-OMe is EDG → destabilizes phenoxide → less acidic than phenol.
- (D) > (A): Phenol derivatives (even with EDG) are more acidic than aliphatic alcohols (resonance delocalization in phenoxide).
- (A) > (B): Methanol > tert-butanol. More alkyl groups increase electron density on O → less stable alkoxide → less acidic. +I effect of 3 methyl groups in tBuOH.
Order: E > C > D > A > B ✓
Key Points to Remember:
- p-Nitrophenol is most acidic (EWG at para with resonance delocalization).
- tert-Butanol is least acidic (3 electron-donating methyl groups destabilize alkoxide).
- All phenols are more acidic than aliphatic alcohols (resonance in phenoxide).
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