Naming Alkenes Using the E,Z System

We have seen that as long as each of the sp carbons of an alkene is bonded to one hydrogen, we can use the terms cis and trans to designate the geometric isomers of an alkene if the hydrogens are on the same side of the double bond, it is the cis isomer if the hydrogens are on opposite sides of the double bond, it is the trans isomer (Section 4.1). 

But how do we designate the isomers of a compound such as l-bromo-2-chloropropene  

Z system of nomenclature was devised for alkenes that do not have a hydrogen attached to each of the sp carbons.  

To name an isomer by the E,Z system, we first determine the relative priorities of the two groups bonded to one of the sp carbons and then the relative priorities of the two groups bonded to the other sp carlx)n. (The rules for assigning relative priorities are explained below.) 

The Z isomer has the high-priority groups on the same side. 

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