Final answer:
Reactions involving a carbonyl group and a strong acid start with the protonation of the carbonyl oxygen, making the carbonyl carbon more electrophilic and susceptible to nucleophilic attack.
Step-by-step explanation:
Any reaction involving a carbonyl group and a strong acid begins with the protonation of the carbonyl oxygen.
Carbonyl compounds such as aldehydes or ketones have a polar C=O bond, due to the difference in electronegativity between carbon and oxygen. When a strong acid is introduced, the oxygen atom with its lone pair of electrons can act as a Lewis base, accepting a proton (hydrogen ion) from the acid. This protonation temporarily increases the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack.
Carboxylic acids are typically prepared by the oxidation of aldehydes or alcohols, where the latter's -OH group must be on the terminal carbon atom within the carbon chain. In the presence of acid, reactions such as acyl substitution can occur with carboxylic acids and their derivatives, mainly due to the electrophilic nature of the carbonyl group enhanced by protonation. Carboxylic acids and ketones often undergo addition reactions initiated by the attack on the electrophilic carbonyl carbon.