Which of the following structures represents a ketone?

• A. A compound with the structure $CH$₃-C(=O)O-H
• B. A compound with the structure $CH$₃-C(=O)-H
• C. A compound with the structure $CH$₃-C(=O)-O-CH₃
• D. A compound with the structure $CH$₃-C(=O)-CH₃

Answer: (D)

Verified step by step guidance

1. Recall the definition of a ketone: a ketone contains a carbonyl group (C=O) bonded to two carbon atoms. This means the carbonyl carbon is connected to two alkyl or aryl groups, not to hydrogen.
2. Examine each given structure and identify the carbonyl group (C=O) in each one.
3. Check the atoms attached to the carbonyl carbon in each structure: if it is bonded to at least one hydrogen, it is not a ketone (it could be an aldehyde or other functional group).
4. For the structure with the carbonyl carbon bonded to two carbon atoms (e.g., two methyl groups, CH3-CO-CH3), recognize this as a ketone because it fits the ketone definition.
5. Exclude structures where the carbonyl carbon is bonded to oxygen or hydrogen atoms, as these represent other functional groups such as carboxylic acids, esters, or aldehydes, not ketones.