Cis-/trans- Designation

How is the cis-/trans- designation for alkenes determined^41.1?

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 cis-. If the converse true, use trans-.