Benzenedicarboxylic acid is a group of chemical compounds which are dicarboxylic derivatives of benzene. Benzenedicarboxylic acid comes in three isomers:

Phthalic acid (1,2-benzenedicarboxylic acid) Isophthalic acid (1,3-benzenedicarboxylic acid) Terephthalic acid (1,4-benzenedicarboxylic acid)

Common NamePhthalic acidIsophthalic acidTerephthalic acidSystematic Name1,2-benzenedicarboxylic acid1,3-benzenedicarboxylic acid1,4-benzenedicarboxylic acidStructural FormulaCAS Registry Number88-99-3121-91-5100-21-0 All isomers share the molecular weight 166.13 g/mol and the chemical formula C8H6O4.