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Although phenoxide ion has more number of resonating structures than carboxylate ion, carboxylic acid is a stronger acid than phenol. Why? |
Answer» Solution :Let us compare the resonating structures of phenoxide and carboxylate ions :  In structures II, III and IV, the negative charge is on less electonegative carbon. THEREFORE, their contribution to the RESONANCE stabilisation is negligible. Thus, structures I and V contribute MAINLY to the resonance stabilisation. Now consider the resonance structures of carboxylate ION  Negative charge on carboxylate ion is delocalised over two oxygen atoms while in structures and of phenoxide ion the negative charge is delocalised over one oxygen atom. Hence, carboxylate ion is stabilised to a GREATER extent. Thus, carboxylic acid is stronger than phenol. |
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