• Cis-trans only work when there is only two elements. If there are three to four elements you are going to use the E and Z isomers. Just like in Cis and Trans isomers, you will find what element has a high atomic number and that element is your priority. Use E isomer if the priority groups are on the opposite side and use Z isomer if the priority groups are on the same side. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

• In this example on the left side the priority is Bromine since Bromine has a high atomic number and on the right side Chlorine is the priority since it has a high atomic number compare to Hydrogen. Since they are on both sides, the isomer that will be used is Z. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

• In this example on the left side the priority is Fluorine since Fluorine has a high atomic number and on the right side Chlorine is the priority since it has a high atomic number than Hydrogen. Since they are on the oppositesides, the isomer that will be used is E. 

 

 

 

 

written by: Bernadeth Castilleja