Question

Whats the difference between ez isomerism and cis and trans isomers? (they both seem to basically have the same rules so i don't get the difference)

Answer 1

They are the same, `"E- "-=" trans-"` and `"Z- "-=" cis-"`. Except E-Z is used for more complex isomers.

Take the two isomers for 1,2-dichloroethene for example:

As each side only has 1 H and 1 Cl atom, you can tell if the Cl atoms are on the same or opposite sides, and therefore decide upon cis- or trans-.

However, if you took:

Each 'corner' has something different, there is nothing to compare each other too. However, EZ notation uses the total atomic mass of each corner to decide upon E- or Z-. In this case, on the left hand side `CH_3CH_2` has a greater mass than `CH_3`, on the right hand side, `CH_2OH` has a greater mass than `COH`. As the heaviest 'corner' on each side is on opposite sides, it is an E- isomer.