Which of the following best explains why phenol reacts with aqueous NaOH, but alcohols do not?
Correct answer: D. Phenol is weakly acidic due to resonance stabilization of phenoxide ion
- A. Phenol has a lower boiling point than alcohol
- B. Alcohols contain a strong O-H bond that cannot be broken by weak bases
- C. Phenol form hydrogen bonding that facilitates ionization
- D. Phenol is weakly acidic due to resonance stabilization of phenoxide ion
Explanation
Losing the hydroxyl hydrogen gives phenol an ion whose negative charge is delocalised into the benzene ring, so the phenoxide ion is far more stable than an alkoxide and the acid dissociates readily enough to be neutralised by sodium hydroxide. An alkoxide has no such delocalisation, so ethanol is not acidic enough to react. Both compounds hydrogen bond, so that cannot be the deciding factor.
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About Phenols
Phenols contain a hydroxyl group directly bonded to an aromatic ring, making them more acidic than alcohols because the phenoxide ion is resonance-stabilised. Reactions include ionisation with bases, electrophilic substitution, bromination, nitration and oxidation, with attention to the difference between phenols and aliphatic alcohols.
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