How can you tell e and z isomers apart?
It is similar to cis (Z) and trans (E) , but are specific for when the substituents are different.
E (german entgegen) means the substituents of higher priority are on the opposite side, and Z (zusammen) when they are on the same side, of the double bond, or cycle.
The priority rules come from the Cahn, Ingold e Prelog rules. It is more or less like this:
1)Higher atomic number of the substituent gives higher priority.
2)If the first element is the same try the following.
3)turn to rule number 1.
Do this until you can atribute the priorities of the four substituents.