cis-Aconitic acid (cis-1-propene-1,2,3-tricarboxylic acid, C6H6O6) cry
stallizes with an intramolecular hydrogen bond between the two carboxy
lic acid groups linked by the C double bond C double bond and exhibits
a complex intermolecular hydrogen-bond pattern. The two carboxylic ac
id groups involved in the intramolecular hydrogen bond are coplanar wi
th the propene skeleton, while the third carboxylic group is twisted o
ut of this plane with a dihedral angle of 66.21 (9)degrees.