Cis and Trans, E and Z Nomenclature

Since double bonds and rings can’t rotate, we need different names for the different arrangements they can create. 

Two groups coming off the same carbon never have a cis/trans relationship. In case you are wondering, they are called geminal (you don’t need to know this yet.) 

E/Z Nomenclature

The cis/trans nomenclature system is awesome, but it breaks down with multisubstituted alkenes. 

So the E/Z naming system allows us to name tri- and tetra- substituted alkenes.

The difference between E and Z

Using the periodic table to assign priorities, trans = E, and cis = Z. 

Example: Assign an (E) – (Z) designation to the following alkenes if applicable


Great! Now let’s combine this with what we’ve learned about functional groups (alkyl halides and alcohols) to name some more complex molecules. 

Problem: Determine the IUPAC name of the following molecule 


This was a great example of how the root chain must always have the functional group within it, even if it is shorter!

Problem: Determine the IUPAC name of the following molecule 


Hope you don’t hate me for throwing two alcohols in there! This is great practice though.