Out of two groups, i.e. —Cl and —CH3 attached to the C−1 atom , the atomic number of Cl is greater than the C-atom of —CH3 group. Hence, here Cl is given priority over —CH3 group. Similarly, out of two groups attached to the C−2 atom i.e., —Br and —CH2CH3 the atomic number of Br is greater than the C atom of —CH2CH3 group. Thus, Br gets priority over C atom of —CH2CH3 group. Hence, the compound
looks like:
It is very clear that the bulky groups are at the same side of the double bond, hence this is a Z-isomer.
