Acid amides

Acid amides may be regarded as the derivatives of carboxylic acids in which -OH part of the carboxylic group is replaced by the -NH₂ group.

Esters are derivatives of the carboxylic acids in which the -OH part of the carboxylic group has been replaced by -OR group where R may be alkyl or aryl group.

Acid anhydrides are considered to be derived from carboxylic acids by the removal of a molecule of water from the two molecules of the acid.