Nomenclature and Structure of Carboxyl Group

The Carboxyl Group

Compounds that carry a $-\text{COOH}$ group are called carboxylic acids. This group is really two familiar groups fused together — a carbonyl ($>\text{C}=\text{O}$) and a hydroxyl ($-\text{OH}$) sharing the same carbon — and that fusion is exactly what gives the functional group its name, carb-oxy-l.

Carboxylic acids come in two broad flavours depending on what is attached to the carboxyl carbon:

• Aliphatic acids, written generally as $\text{R}-\text{COOH}$, where R is an alkyl group.
• Aromatic acids, written generally as $\text{Ar}-\text{COOH}$, where Ar is an aryl (benzene-ring-based) group.

Where They Occur

Carboxylic acids are one of the most widespread functional groups in nature — a large number of naturally occurring compounds carry this group. A particularly important set are the higher aliphatic acids in the $\text{C}_{12}$–$\text{C}_{18}$ range, known as fatty acids. These do not usually occur free; they are found locked up as esters of glycerol inside natural fats and oils. …