What are the isomers of dibromoethene (C2H2Br2) and how do their polarities differ?

Dibromoethene (C2H2Br2) can exist in three different isomeric forms: 1,1-dibromoethene, cis-1,2-dibromoethene, and trans-1,2-dibromoethene. Below are the Lewis structures for each isomer along with their polarities.

1. 1,1-Dibromoethene

Polarity: Nonpolar

   H        Br
    \      /
     C == C
    /      \
   H        Br

In 1,1-dibromoethene, both bromine atoms are attached to the same carbon atom. The molecule is symmetrical, resulting in no net dipole moment, hence it is nonpolar.

2. Cis-1,2-Dibromoethene

Polarity: Polar

      Br     H
       \   /
        C == C
       /   \
      H     Br

For cis-1,2-dibromoethene, the bromine atoms are on the same side of the double bond. This arrangement leads to an uneven distribution of charge, creating a net dipole moment, making it a polar molecule.

3. Trans-1,2-Dibromoethene

Polarity: Polar

      H     Br
       \   /
        C == C
       /   \
      Br     H

In trans-1,2-dibromoethene, the bromine atoms are located on opposite sides of the double bond. Although it may appear symmetric, the presence of the bromine atoms still creates a dipole due to the difference in electronegativity between the carbon and bromine atoms, resulting in a polar molecule.

In summary, the first isomer, 1,1-dibromoethene, is nonpolar due to its symmetrical structure, while both cis-1,2-dibromoethene and trans-1,2-dibromoethene are polar due to their asymmetrical arrangements of bromine atoms.