Question

Which of the following has zero dipole moment?

• A. cis-2-butene
• B. trans-2-butene
• C. 1-butene
• D. 2-methyl-1-propene

Answer 1

The correct option is B trans-2-butene

Trans has no (or zero) dipole moment than cis isomer.
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, thus cis isomer is more polar than trans.
In the trans isomer, the terminal groups are on the opposite sides of the double bond. So, here the dipole moments of the trans isomer is zero.