Both aliphatic carboxylic acid (R- COOH) and phenol have tendency to release protons as follows
Both carboxylate ion and phenoxide ion are resonance stabilised as explained :
Although phenoxide ion has more number of resonating structure (five) than carboxylate ion (two), yet carboxylate ion is better resonance stabilised than phenoxide ion. It is due to the following two facts.
1. The two contributing structure of carboxylate ion are structurally equivalent, but not in the case of phenomide ion
2. In carboxylate ion the negative charge is dispersed over two oxygen atoms, where as in phenoxide ion, in three out of five resonance structure, the negative charge is less on less electronegative carbon atom.
Due to better resonance stabilisation of carboxylate ion the equilibrium is shifted more towards the right hand side in case of carboxylic acid than in phenol. Therefore carboxylic acid have a greater tendency to release the proton. That is carboxylic acid is more acidic than phenol.
