question_answer 27)

Although phenoxide ion has more number of resonatingstructures than carboxylate ion, carboxylate acid is a stronger acid thanphenol. Why? Comparative effectiveness of delocalization of- negative charge isresponsible for the acidic strength. A resonating structure havingnegative charge on more electronegative atom, is more stable.  

Answer:

1. Phenoxide ion has non-equivalent resonance structures inwhich the negative charge is at the less electronegative carbonatom. 2. The negative charge is delocalized over two electronegative oxygen atoms in carboxylate ion whereas in phenoxide ion the negative charge less effectively delocalized over one oxygen atom and less electronegative carbon atoms.