Which functional group is highest on the MCAT functional group hierarchy?

The functional group that sits highest on the hierarchy of functional groups is the carboxylic acid. This ranking is based on the functional groups' reactivity, priority in nomenclature, and the strength of their acidic properties.

Carboxylic acids contain both a carbonyl group (C=O) and a hydroxyl group (–OH) on the same carbon atom. This structure allows them to exhibit both acidic characteristics, due to the presence of the hydroxyl group that can release a proton (H+), making carboxylic acids some of the most valuable and reactive functional groups in organic chemistry.

Additionally, in naming organic compounds, functional groups with higher priority generally determine the suffix of the compound’s name. Carboxylic acids are designated with the suffix "-oic acid," which gives them a higher priority over alcohols, aldehydes, and amines, which have lower priority designations like "-ol," "-al," and "-amine," respectively.

The unique properties of carboxylic acids, such as their ability to participate in hydrogen bonding (due to the –OH group), further enhance their importance and signal their high position in the functional group hierarchy. This is why carboxylic acids are