Question

The ionization constant of phenol is higher than that of ethanol because :

• A. Phenoxide ion is bulkier than ethoxide
• B. Phenoxide ion is stronger base than ethoxide
• C. Phenoxide ion is stabilized through delocalization
• D. Phenoxide ion is less stable than ethoxide

Answer 1

Answer: (C)

The acidic nature of phenol is due to the formation of stable phenoxide ion in solution
$C_6{H}_{5}OH+H_{2}O\rightleftharpoons \underset{\text{ Phenoxide ion}}{C_6{H}_5{O}^{-}}+H_3{O}^{+}$
The phenoxide ion is stable due to resonance.
The negative charge is delocalized in the benzene ring which is a stabilizing factor in the phenoxide ion and increase acidity of phenol. whereas no resonance is possible in alkoxide ions $(RO-)$ derived from alcohol. The negative charge is localized on oxygen atom. Thus, alcohols are not acidic.