Each substituent on a double bond is assigned a priority based on the Cahn-Ingold-Prelog priority rules. Ligands with highest priorities define the reference frame. If the two groups of higher priority are on opposite sides of the double bond (trans arrangement), then the E configuration is assigned to the bond. If the two groups of higher priority are on the same side of the double bond (cis arrangement), than the Z configuration is assigned to it.
EZConfiguration.NONE: if no stereo information given or the double bond doesn't have enough ligands to be stereochemically active
EZConfiguration.CIS: for configuration Z if the ligands with highest priority are on the same side of the double bond
EZConfiguration.TRANS: for configuration E if the ligands with highest priority are on the opposite side of the double bond
EZConfiguration.E_OR_Z: if the ligands can arrange both E and Z
Setting E/Z information
The stereoisomer type can not be modified directly. However, it is possible to change it through changing cis/trans information of the double bond using the methods mentioned in Setting cis/trans information in 0 Dimension and Setting cis/trans information in 2 or 3 Dimension. If the opposite value is needed then the one actually set, cis/trans information should be changed to the opposite value also. The removal of cis/trans information also removes the E/Z information.
Getting E/Z information
The E/Z stereoinformation can be calculated by the getStereo2(MolBond b) function of the MoleculeGraph class.
MolBond b = molecule.getBond(
EZConfiguration ez = molecule.getEZStereo(b);
ez = EZConfiguration.Z