Question

Why is Phenol more acidic than alcohols?

Hint:

Phenol is more acidic because its conjugate base is resonance-stabilized, while alcohols form unstable alkoxide ions.

Answer 1

Concept: Acidity depends on the stability of the conjugate base formed after the loss of a proton. Greater stability of the conjugate base leads to higher acidity.
Step 1: Formation of conjugate bases.

• Phenol loses H$^+$ to form phenoxide ion (C$_6$H$_5$O$^-$)
• Alcohols lose H$^+$ to form alkoxide ions (RO$^-$)

Step 2: Resonance stabilization in phenol. The negative charge on the oxygen atom in the phenoxide ion is delocalized over the aromatic ring through resonance. This distribution of charge stabilizes the conjugate base.
Step 3: Lack of resonance in alcohols. Alkoxide ions do not have resonance stabilization. The negative charge remains localized on the oxygen atom, making them less stable.
Step 4: Effect of hybridization. In phenol, the oxygen is attached to an sp$^2$-hybridized carbon of the benzene ring, which has a higher electronegativity than the sp$^3$ carbon in alcohols, further stabilizing the phenoxide ion.
Conclusion: Due to resonance stabilization and the influence of the aromatic ring, phenoxide ions are more stable than alkoxide ions, making phenol more acidic than alcohols.