Which functional group is associated with esters?

• A. R(C=O)H
• B. RCO2R'
• C. RCO2H
• D. R(C=O)R'

Answer: (B)

Esters are characterized by their functional group, which is defined by the presence of a carbonyl group (C=O) adjacent to an ether component (an alkoxy group, -O-R). The general structure of an ester can be represented as RCOOR', where R and R' are hydrocarbon chains or groups.

The specific choice that represents this structure is the one that includes the carbonyl group directly bonded to an oxygen atom, which then connects to another hydrocarbon group. This configuration is characteristic of esters, as they are formed from the reaction of an alcohol and a carboxylic acid, leading to the formation of this specific functional group.

The presence of the carbonyl and the ether part together is crucial for the reactivity and properties of esters, which are important in various biological and chemical processes, including the formation of lipids in biological systems.