What is the general structure of an ester?

The general structure of an ester is represented as R-C=O-O-R'. In this structure, "R" and "R'" denote hydrocarbon chains or groups, which can be either alkyl or aryl in nature. The carbonyl group (C=O) is bonded to an oxygen atom that connects to another carbon chain (the alkoxy group, represented as -O-R'). This specific arrangement is characteristic of esters, which are derived from carboxylic acids and alcohols through a condensation reaction.

Esters are widely recognized for their fruity aromas and are commonly found in nature as well as used in the production of fragrances, flavorings, and solvents. The presence of the carbonyl and ether-like linkage (C-O) is what differentiates them from other functional groups.

The other options reflect different organic compounds: one represents a carboxylic acid (R-C=O-OH), another depicts an alkene (R-C=C-R'), and the last one signifies a primary amine (R-NH₂). None of these structures encompass the defining features of an ester, which solidifies why the correct option is the one showcasing the ester functionality.