29. Since carboxyl group consists of carbonyl and hydroxyl groups, it is expected that acids show reactions due to both these groups. However the reactions expected of these groups are modified as a result of interaction between these groups due to close proximity. Carboxylic acids are resonance hybrid of the following structures. It is clear that the carbonyl part of the carboxyl group does not have a double bond character but a reduced double bond character. Thus it does not give the reactions of the carbonyl group. The carbonyl carbon in carboxyl group is less electrophilic than the carbonyl carbon in aldehydes and ketones due to resonance. Therefore many nucleophilic addition reactions of aldehydes and ketones do not take place with carboxylic acids. The same effect makes the hydroxyl group of carboxylic acids more acidic than the hydroxyl group of alcohols and phenols justifying why they are called acids.