why is cis e exponent
The E-Z system. The problem with the cis-trans system for naming geometric isomers. Consider a simple case of geometric isomerism which we've already discussed on the previous page. You can tell which is the cis and which the trans form just by looking at them. All you really have to remember is that trans means across (as in transatlantic or transcontinental) and that cis is the opposite. It is a simple and visual way of telling the two isomers apart.