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First, let's draw the Lewis structures for the three possible isomers of dichloroethylene (C2H2Cl2), having a carbon-carbon double bond. Isomer 1 (1,1-Dichloroethylene): ``` Cl Cl | | H-C=C-H or H-C=C-Cl ``` Isomer 2 (cis-1,2-Dichloroethylene): ``` Cl H | | H-C=C-Cl or H-C=C-H ``` Isomer 3 (trans-1,2-Dichloroethylene): ``` Cl Cl | | H-C=C-H or H-C=C-Cl ```

To figure out which isomer has a zero dipole moment, let's compare the dipole vectors for the three isomers. In the 1,1-Dichloroethylene isomer, the two C-Cl bonds have dipole moments that point in opposite directions (towards the more electronegative Cl), canceling each other out, giving a zero net dipole moment. cis-1,2-Dichloroethylene has the Cl atoms on the same side of the double bond. This makes the molecule's dipole moments not cancel each other out, producing a nonzero net dipole moment. In trans-1,2-Dichloroethylene, the two C-Cl bonds are on opposite sides of the double bond, which makes their dipole moments cancel each other out, resulting in a zero net dipole moment. Thus, 1,1-Dichloroethylene and trans-1,2-Dichloroethylene isomers have a zero dipole moment.

Now let's analyze Chloroethylene (C2H3Cl) for its possible isomeric forms. There are two possible isomers for Chloroethylene: Isomer 1 (vinyl chloride or H2C=CH-Cl): ``` Cl H | | H-C=C-H or H-C=C-H ``` Isomer 2 (chloroethene or Cl-C=C-H): ``` Cl Cl | | H-C=C-H or H-C=C-Cl ``` Both isomers have a net dipole moment, nonzero, as the C-Cl bond creates a dipole due to the electronegativity difference between Cl and C, and no other atoms cancel it out. So yes, they would be expected to have dipole moments.