Which class of compounds are characterized by a carbonyl group bonded to two carbon atoms?

The class of compounds characterized by a carbonyl group bonded to two carbon atoms is known as ketones. In ketones, the carbonyl group (C=O) is situated within the carbon chain, connected to two other carbon atoms. This structural feature differentiates ketones from other carbonyl-containing compounds. For instance, aldehydes have a carbonyl group at the end of a carbon chain, meaning they bond to at least one hydrogen atom and one carbon atom, which does not match the criteria given in the question.

Ethers and esters, while they contain oxygen, do not have a carbonyl group as their defining feature. Ethers typically consist of an oxygen atom bonded to two alkyl or aryl groups, while esters have a carbonyl group attached to an oxygen atom that is also bonded to a carbon chain, indicating they are derived from carboxylic acids. Therefore, ketones are specific in having the carbonyl group between two carbon atoms, aligning perfectly with the description provided.