Why is phenol substantially more acidic than aliphatic alcohols like ethanol?
Answer and explanation
Correct answer: A. The phenoxide ion is resonance-stabilized over the aromatic ring
- Step 1: Upon deprotonation, phenol forms the phenoxide ion ().
- Step 2: The negative charge on phenoxide is delocalized over the ortho and para positions of the benzene ring through resonance, stabilizing the conjugate base.
- Step 3: In contrast, the ethoxide ion localized on ethanol is destabilized by the inductive effect of the ethyl group.
Answer
The phenoxide ion is resonance-stabilized over the aromatic ring.
Why not the others: Molecular mass does not govern acidity; intramolecular hydrogen bonding occurs in ortho-nitrophenol; and the hydroxyl in phenol is bonded to an sp2 carbon.
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