Which of the following has E- configuration ?

Question

Accepted Answer

Option 1, (E)-1-Bromo-1,2-dichloroethene, is the correct answer because it describes a compound with an E-configuration. In organic chemistry, the E- (from the German "entgegen") configuration refers to the arrangement of substituents around a double bond where the highest priority groups on each carbon are on opposite sides.

1. **Explanation for Option 1:**
   - In (E)-1-Bromo-1,2-dichloroethene, the double bond is between the two carbon atoms. The substituents on these carbons are bromine and chlorine atoms. According to the Cahn-Ingold-Prelog priority rules, bromine has a higher priority than chlorine due to its higher atomic number. Therefore, on one carbon, bromine is the highest priority group, and on the other carbon, chlorine is the highest priority group. In the E-configuration, these highest priority groups (bromine and chlorine) are on opposite sides of the double bond, confirming the E-configuration.

2. **Explanation for why other options are incorrect:**
   - **Option 2: (Z)-1-Bromo-1,2-dichloroethene** describes a Z-configuration, where the highest priority groups on each carbon are on the same side of the double bond. This is contrary to the E-configuration, which requires them to be on opposite sides.
   - **Option 3: (E)-2-Bromo-1-chloro-1-methylethene** involves a different compound where the substituents and their arrangement around the double bond do not match the description of (E)-1-Bromo-1,2-dichloroethene. The presence of a methyl group changes the priority and spatial arrangement, making it a different compound.
   - **Option 4: (Z)-2-Bromo-1-chloro-1-methylethene** similarly describes a Z-configuration for a different compound, where the highest priority groups are on the same side, not matching the E-configuration required for the correct answer.

In conclusion, Option 1 is the correct choice because it accurately describes a compound with an E-configuration, where the highest priority substituents are on opposite sides of the double bond.