The hydroxyl group in phenol is directly attached to the sp² hybridized carbon of the benzene ring, acting as an electron-withdrawing group. This, along with resonance structures, results in a positive charge on the oxygen, making phenols stronger acids than alcohols.
Why does the hydroxyl group in phenol contribute to its acidic nature, and how is it different from alcohols?
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The hydroxyl group in phenol contributes to its acidic nature due to resonance stabilization. In phenol, the oxygen lone pair delocalizes into the aromatic ring through resonance, stabilizing the phenoxide ion. This resonance effect facilitates the release of a proton (H⁺), resulting in phenol’s weak acidic behavior. This is different from alcohols where resonance stabilization is not significant, making alcohols weaker acids compared to phenols. The presence of a conjugated aromatic system in phenol enhances the stability of the anion, making the hydroxyl group more acidic in the context of phenolic compounds.