Question

Two isomers of 1,2 Dichloroethene are known. One has dipole moment of 2.4 D; the other has zero dipole moment. Draw the two isomers, and explain why one has zero dipole moment

CHCl=CHCl (1,2 Dichloroethene)

Short answer

1,2 Dichloroethene has two isomers i.e. cis- and trans-1,2 Dichloroethene, both have different physical properties. Cis isomer has net dipole moment whereas dipole moment in trans isomer cancels and has zero dipole moment.

Cis-1,2-dichloroethene trans-1,2-dichloroethene

Step-by-step solution

Step-1

Cis isomer has dipole moment because two C-Cl bond are on same side therefore they strengthen each other as a result of which it is polar.

Step-2

Whereas trans isomer has two C-Cl bond moment opposite to each other, which cancels the dipole moment and net dipole moment is zero.