A type of stereoisomer in which a chemical group or atom occupies different spatial positions in relation to the double bonds. If the double bond is between two carbon atoms, the isomers are called cis and trans, as in crotonic acid, where the H and COOH reverse locations:
If the double bond is between a nitrogen and a carbon atom, the isomers are named anti and syn, as in benzaldoxime, where the OH group shifts locations.
This phenomenon also occurs in saturated ring compounds having three or more members in the ring, as well as in certain coordination compounds.See Stereochemistry.