二羧酸是指含有两个羧基官能团的有机化合物，分子通式常写为HOOC-R-COOH。可以使用二羧酸来制备共聚物，比如聚酰胺、聚酯等。

A dicarboxylic acid is an organic compound containing two carboxyl functional groups (-COOH). The general molecular formula for dicarboxylic acids can be written as HO₂C-R-CO₂H, where R can be aliphatic or aromatic. In general, dicarboxylic acids show similar chemical behavior and reactivity to monocarboxylic acids. Dicarboxylic acids are also used in the preparation of copolymers such as polyamides and polyesters. The most widely used dicarboxylic acid in the industry is adipic acid, which is a precursor used in the production of nylon. Other examples of dicarboxylic acids include aspartic acid and glutamic acid, two amino acids in the human body.