Which description defines the carboxyl functional group?

Which description defines the carboxyl functional group?

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

Answer: (B)

The carboxyl group is a carbonyl carbon (C=O) bonded to a hydroxyl group (OH), written as -COOH. That exact combination is what the description C=O + OH (COOH) captures, making it the correct match. The other descriptions point to different functionalities: a carbonyl with an alkoxy group (COO-R) is an ester, not a carboxyl; OH alone is simply a hydroxyl group; and a nitrogen-containing group refers to amines or amides. Carboxyl groups are common in organic acids and can donate a proton, giving characteristic acidity seen in many biological molecules.

The carboxyl group is a carbonyl carbon (C=O) bonded to a hydroxyl group (OH), written as -COOH. That exact combination is what the description C=O + OH (COOH) captures, making it the correct match. The other descriptions point to different functionalities: a carbonyl with an alkoxy group (COO-R) is an ester, not a carboxyl; OH alone is simply a hydroxyl group; and a nitrogen-containing group refers to amines or amides. Carboxyl groups are common in organic acids and can donate a proton, giving characteristic acidity seen in many biological molecules.