Which option describes an ester functional group?

Which option describes an ester functional group?

• A. C=O + O-R (COO-R)
• B. C=O + OH (COOH)
• C. OH alone
• D. N-containing group

Answer: (A)

An ester has a carbonyl carbon double-bonded to oxygen and single-bonded to an alkoxy group (-O-R). That gives the C=O together with an O-R attachment, often shown as COO-R. So describing C=O plus O-R captures the ester structure precisely. A carboxylic acid would instead have C=O with an OH group, not O-R; an OH group by itself is just a hydroxyl, and a nitrogen-containing group is not an ester.

An ester has a carbonyl carbon double-bonded to oxygen and single-bonded to an alkoxy group (-O-R). That gives the C=O together with an O-R attachment, often shown as COO-R. So describing C=O plus O-R captures the ester structure precisely. A carboxylic acid would instead have C=O with an OH group, not O-R; an OH group by itself is just a hydroxyl, and a nitrogen-containing group is not an ester.