When a carbonyl group is added to various functional groups, significant changes occur in their chemical properties and classifications. For instance, when a carbonyl is introduced to an alcohol, the resulting structure features a carbonyl (C=O) adjacent to a hydroxyl group (–OH). This transformation leads to the formation of a carboxylic acid, which is a fundamental acid in organic chemistry. The condensed structural formula for a carboxylic acid is typically represented as COOH or C(=O)OH. It is crucial to memorize these representations, as they are commonly encountered in organic chemistry.

Similarly, when a carbonyl is added to an amine, the resulting compound is known as an amide. The structure consists of a carbonyl group bonded to a nitrogen atom (–NH₂), and its condensed formula can be expressed as C(=O)NH₂ or C(=O)NHR, where R represents any additional hydrogen atoms or carbon groups attached to the nitrogen. The degree of the amide is determined by the number of carbon groups attached to the nitrogen; for example, a cyclic amide, also known as a lactam, is classified as a secondary amide because the nitrogen is bonded to two carbon groups.

Lastly, when a carbonyl is added to an ether, the product formed is an ester. The ester functional group is characterized by a carbonyl group bonded to an alkoxy group (–OR), with the condensed formula represented as C(=O)O-R or C(=O)O-R. Recognizing these structural formulas is essential for understanding the relationships between different organic compounds and their reactivity.