Question

Why do carboxylic acid show higher co frequency than ester

Answer 1

Answer:

Although a phenoxide ion has a higher number of resonating structures than carboxylate ions carboxylic acid is a stronger acid than phenol.

Answer 2

This would seem to suggest that the acid decreases the carbonyl bond strength and the ester weakens it. Presumably this is also linked to the relative electrophilicity of the ester and the acid.