E-Z notation

The stereochemistry of highly substituted alkenes cannot be defined as cis or trans. For this purpose a new notation known as E-Z notation is used. Following a set of rules (Cahn-Ingold-Prelog rules) the substituents on a double bond are assigned priorities. The double bond is assigned the configuration E,(from entgegen, the German word for opposite) if the two groups of higher priority are on the opposite sides of the double bond. On the other hand, the double bond is assigned the configuration Z (from zusammen, the German word for together) if the two groups of higher priority are on the same side of the double bond.