Question

Which one of the following compounds has the highest dipole moment?

• A. cis-1,2-dichloroethene
• B. trans-1,2-dichloroethene
• C. Both (a) and (b) has same dipole moment
• D. Cannot be determined

Answer 1

The correct option is A cis-1,2-dichloroethene

Cis isomer has more dipole moment than trans isomer, because it has two similar groups on same side of double bond. So the dipole gets added up and resultant dipole moment is large. Whereas in trans isomers the group were arranged on opposite side so their dipole moments will get cancel with each other and shows zero dipole moment. Hence, cis isomer is more polar than trans.
Thus cis-1,2-dichloroethene has the larger dipole moment than trans-1,2-dichloroethene.