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Question
Compare acidity of phenol with that of ethanol.
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Solution 1
Phenol is more acidic than ethanol. This is because the phenoxide ion obtained after the release of a proton from phenol becomes stable through resonance, whereas the ethoxide ion (after the release of a proton from ethanol) is not stable.
Solution 2
Compared with ethanol, phenols are more acidic. They lose their H atom as H+ more readily than alcohols. The behaviour of phenol can be attributed to resonance stabilisation arising from the contributing structures of the corresponding phenoxide ion.
The resonance stabilisation from the contributing structures (I)-(V) sufficiently offsets the O–H bond dissociation energy, rendering phenol acidic.
No resonance structures exist for the ethoxide ion; hence, the conversion of ethanol to ethoxide is not encouraged under standard conditions. Therefore, ethanol exhibits lower acidity compared to phenol.
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