E & Z Designation

What is E & Z designation?

Another system to designate the location of substituent groups across a carbon-carbon double bond.

How do you determine E or Z nomenclature of alkenes?

1. Assign priority to the groups attached to each end of the double bond.
   • Priority is assigned on the basis of atomic weight: high atomic weight, high priority.
   • If two groups have the same atomic number, move outward for each group and then compare the atomic number:
2. If the higher priority group for one end of the C=C is on the same side as the highest priority group for the other end, use Z. If the substituent groups on either end are on opposite sides, use E^41.2.

Figure 40.5: Cis-/trans- alkenes: cis- (Z) and trans- (E) designations