What is the structural representation of a carboxyl group?

The carboxyl group is a functional group characterized by its structure, which consists of a carbon atom that is double-bonded to an oxygen atom and also single-bonded to a hydroxyl group (–OH). This is represented as R-COOH, where R represents a hydrocarbon chain or another group that is attached to the carboxyl group.

This representation illustrates that the carboxyl group contains both a carbonyl (C=O) and a hydroxyl (–OH) component, making it a key characteristic in organic compounds, particularly in amino acids and fatty acids. The presence of the –COOH group is what distinguishes carboxylic acids from other functional groups, giving them acidic properties.

In contrast, the other options highlight different functional groups: C=O denotes a carbonyl group, R-NH2 represents an amine group, and R-OH indicates an alcohol group. None of these structures reflect the complete configuration of the carboxyl group, which explicitly incorporates both the carbonyl and hydroxyl elements. Thus, R-COOH accurately conveys what defines a carboxyl group in structural terms.