Determination of E and Z isomers
for alkenes

  1. The priority of a groups depends upopn the atomic number of the atom attached to the double bond. The higher the atomic number, the higher the priority of the group is.
  2. If two atoms with the same priority are bound to the carbon atom of the double bond, a search is made along each group, moving away from the double bond until a difference is found, and priority is assinged on the basis of that difference.
  3. The double bond is assigned a Z (for zusammen, German for together) configuration when the two groups with the higher priority at each end of the doube bond are on the same side of the molecule. If the two groups of higher priority are on opposite sides of the double bond, the molecule is given an E (for entgegen, German for opposite) configuration.