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Explain why hydroxyl group attached to an aromatic ring is more acidic than the one in which hydroxyl group is attached to an alkyl group?

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Hydroxyl group attached to an aromatic ring is more acidic than the one in which hydroxyl group is attached to an alkyl group. Phenols are a million times more acidic than alcohols.

In alcohols, group is attached to atom which is hybridised. In phenols, group is attached to atom which is hybridised.  hybridised atom is more electronegative than hybridised. Thus electron density on atom in phenol is lower than the electron density on atom in alcohol. Hence, the polarity of bond and ionization in phenol is more than that in alcohol.

Also when alcohols lose a proton, the resulting alkoxide ion has negative charge localised on atom. However when phenols lose a proton, the resulting phenoxide ion has negative charge of  atom  delocalised  over ortho and para positions of aromatic ring. Hence, phenoxide ion is more stable than alkoxide ion.

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