Which option represents the carboxyl functional group?

Which option represents the carboxyl functional group?

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

Answer: (D)

Carboxyl groups are defined by a carbon atom double-bonded to oxygen and single-bonded to a hydroxyl group, giving the -COOH arrangement. This combination—C=O with an OH on the same carbon—is what distinguishes carboxyl groups from others. The OH can donate a proton, and the resulting negative charge on the oxygen is stabilized by resonance with the carbonyl, making carboxylic acids acidic. An OH by itself is just a hydroxyl group (as in alcohols), a standalone C=O is a carbonyl group found in aldehydes and ketones, and a nitrogen-containing group points to amines or amides, not carboxyl.

Carboxyl groups are defined by a carbon atom double-bonded to oxygen and single-bonded to a hydroxyl group, giving the -COOH arrangement. This combination—C=O with an OH on the same carbon—is what distinguishes carboxyl groups from others. The OH can donate a proton, and the resulting negative charge on the oxygen is stabilized by resonance with the carbonyl, making carboxylic acids acidic. An OH by itself is just a hydroxyl group (as in alcohols), a standalone C=O is a carbonyl group found in aldehydes and ketones, and a nitrogen-containing group points to amines or amides, not carboxyl.