MCAT Chemical and Physical Foundations of Biological Systems Practice Exam 2025 – Comprehensive All-in-One Guide for Exam Success!

The correct choice for the prefix used for ketones is "oxo-." In organic chemistry, ketones are characterized by the presence of a carbonyl group (C=O) attached to two carbon atoms, making them structurally distinct. The "oxo-" prefix is specifically used to denote the presence of a carbonyl group within a compound when naming, particularly if the carbonyl group is not at the terminal position of the carbon chain, as would be the case in aldehydes.

For instance, in a compound where a carbonyl group is attached to the second carbon of a longer carbon chain, the ketone can be named using the "oxo-" prefix along with the main chain name. This is consistent with the IUPAC naming conventions which help in identifying functional groups clearly. The choice of "oxo-" helps to avoid confusion that could arise from terms that might imply different functionalities.

Other prefixes such as "hydroxy-" refer to alcohols, "alkoxy-" indicates ethers, and "carboxy-" pertains to carboxylic acids, which are all unrelated to the naming of ketones. This specificity is essential for accurately communicating chemical structures in organic chemistry.