14.1:
Carboxylic Acid Derivatives: Overview
The general formula of a carboxylic acid is RCOOH. Here, an acyl group is attached to a hydroxyl group by a single bond.
Carboxylic acid derivatives are compounds where the hydroxyl group is replaced by other functional groups.
For example, replacing the hydroxyl group with a halide forms acyl halides like acetyl chloride, and substitution with an amino group gives amides such as acetamide and cyclic amides like caprolactam.
Similarly, replacing the hydroxyl group with an alkoxy group yields esters such as methyl acetate and cyclic esters like caprolactone.
Furthermore, substitution with an acyloxy group forms acid anhydrides like acetic anhydride and cyclic analogues like succinic anhydride.
Thus, each derivative contains an acyl group attached to a heteroatom.
However, nitriles are also classified as carboxylic acid derivatives, although they lack an acyl group. Instead, they contain a cyano group where a carbon atom is triply bonded to a nitrogen atom, such as acetonitrile.
14.1:
Carboxylic Acid Derivatives: Overview
Carboxylic acid derivatives are formed by replacing the hydroxyl group of carboxylic acids with a different functional group. The most common carboxylic acid derivatives are:
| Acid halides | Acid anhydrides | Esters | Amides |
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Cyclic esters and cyclic amides are referred to as lactones and lactams, respectively.
All carboxylic acid derivatives contain a carbonyl group. However, nitriles have a cyano group where a carbon atom is triply bonded to a nitrogen atom.
Carboxylic acid derivatives in nature
Amongst the acid derivatives, acid halides and acid anhydrides are not commonly found in nature. Esters are more widespread and found in naturally occurring fats and oils. They are also responsible for the characteristic fragrance of fruits and flowers. Some examples of naturally occurring esters include:
| Methyl butanoate | Isopentyl acetate | Butyl Acetate |
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Amides linkages are most common in biomolecules. For example, proteins are composed of repeating amino acid units linked by an amide (CO–NH) bond.
