When aquious bromine is added to aqueous phenol a creamy white ppt is obtained. What does this reaction show ?
Correct answer: C. a hydroxy group makes the benzene ring more susceptible to electrophilic attack
- A. phenol is unsaturated
- B. 2-bromophenol is insoluble in water
- C. a hydroxy group makes the benzene ring more susceptible to electrophilic attack
- D. acid-base reaction
Explanation
The hydroxy group donates electron density into the benzene ring by resonance, activating the ring and directing electrophilic substitution mainly to the 2 and 4 positions. Bromine water therefore gives the readily formed 2,4,6-tribromophenol precipitate. The likely mistake is choosing a, because bromine decolourisation is associated with unsaturation, but this reaction is primarily an activated electrophilic substitution of phenol.
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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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