How is the functional group of an ester represented in a structure?

The representation of the functional group of an ester is depicted as RCOOR'. In this notation, "R" and "R'" signify hydrocarbon chains or groups, while "CO" indicates the carbonyl group (C=O) bonded to oxygen. Therefore, the structure illustrates that an ester consists of a carbonyl group bonded to an alkoxy group (the R' part), which is derived from an alcohol. This structure captures the essence of esters, which are formed through the reaction of a carboxylic acid and an alcohol, resulting in this specific bonding arrangement.

The other choices do not accurately represent the structure of an ester. The option RCOOH refers to a carboxylic acid, highlighting the presence of an -OH group directly attached to the carbonyl carbon. RCHO represents an aldehyde, with a carbonyl group attached to a hydrogen, denoting a different functional group. Lastly, RNCOR' indicates an amide functional group, characterized by a nitrogen atom attached to a carbonyl, which is distinct from the structure of an ester. Thus, A is correctly identified as the representation of an ester functional group.