The two stereoisomers of 1 - bromo-1, 2-dichloroethene can - not be designated as cis and trans in the normal way because the double bond is trisubstituted. They can, however, be given ( E) and (Z) designations. Write a structural formula for each isomer and give each the proper designation.

The two stereoisomers of 1 - bromo-1, 2-dichloroethene can - not be de

1.	The two stereoisomers of 1 - bromo-1, 2-dichloroethene can - not be designated as cis and trans in the normal way because the double bond is trisubstituted. They can, however, be given ( E) and (Z) designations. Write a structural formula for each isomer and give each the proper designation.
Answer» Solution :We write the structures (below), then note that chlorine has a HIGHER priority than hydrogen, and bromine has a higher priority than chlorine. Thegroup with higher priority on C1 is bromine and the GROUP with higher priority at C2 is chlorine. In the first structure the higher priotrity chlorine and bromine atoms are on opposite sides of the doube bond, and therefore this ISOMER is ( E). In the second structure those chlorine and bromine atoms are on the same side, so the LATTER isomer is (Z).