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AAT Bioquest

Why is the acidity of phenols is higher in comparison to alcohols?

Posted February 14, 2023


Answer

Phenols are more acidic than alcohols due the stabilization of the phenoxide ion through resonance. The presence of the electron withdrawing group increases acidity of phenol by stabilizing the phenoxide ion. In contrast, the presence of electron donating groups decreases acidity of phenol through destabilization. More specifically, phenols are more acidic than alcohols because of the negative charge in the phenoxide not being localized on the oxygen atom as it is in an alkoxide ion. The negative charge is delocalized by carbon atoms in the benzene ring. The negative charge can delocalize and spread to reach a lower energy if it is adjacent to a pi electron system, like a positive charge can if it is adjacent to a double bond.   

Additional resources

Phenol

Phenol Red, sodium salt *CAS 34487-61-6*