- Effect of Substituents on the Acidity of Phenol- The acidity of phenol is influenced by substituents on the aromatic ring, which either increase or decrease acidity based on their electronic effects.
Electron-Withdrawing Groups (EWGs)- One effect of substituents on the acidity of phenol:
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- Examples: Nitro (-NO₂), cyano (-CN), carboxyl (-COOH), halogens (-Cl, -Br).
- Effect: Increase acidity.
- Mechanism: EWGs stabilize the phenoxide ion by withdrawing electron density through inductive or resonance effects, making it easier for phenol to lose a proton.
- Position Dependence:
- Ortho- and Para- Positions: Strongly increase acidity via resonance.
- Meta- Position: Less pronounced effect, primarily inductive.
- Example: p-Nitrophenol is more acidic than phenol due to the nitro group.
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Electron-Donating Groups (EDGs):
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- Examples: Alkyl (-CH₃), amino (-NH₂), hydroxyl (-OH), alkoxy (-OCH₃).
- Effect: Decrease acidity.
- Mechanism: EDGs donate electron density, destabilizing the phenoxide ion and making it harder for phenol to lose a proton.
- Position Dependence:
- Ortho- and Para- Positions: Significantly reduce acidity via resonance.
- Meta- Position: Less effect, primarily inductive.
- Example: p-Cresol (4-methylphenol) is less acidic than phenol due to the methyl group.
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