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Question
Answer in brief.
Explain why phenol is more acidic than ethyl alcohol.
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Solution
The difference in the acidic character of phenols and alcohol is due to the difference in reactivity of these compounds towards the ionization of the O–H bond. This can be explained as follows:
i. Ionization of alcohols is represented by the following equilibrium
\[\ce{\underset{\text{Alcohol}}{R - OH} + H2O ⇌ \underset{\text{Alkoxide}}{R - O-} + H3O+}\]
The electron-donating inductive effect (+I effect) of the alkyl group destabilizes the alkoxide ion (the conjugate base of alcohol). As a result, alcohol does not ionize much in the water, and behaves like a neutral compound in an aqueous medium.
ii. Ionization of phenol is represented by the following equilibrium
Phenoxide ion, the conjugate base of phenol, is resonance stabilized by delocalization of the negative charge. Therefore, phenol ionizes in an aqueous medium to a moderate extent. Thus phenols are more acidic than ethyl alcohol.
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