Question

Which of the following statements is not true regarding the cis and trans isomers of 2-butene ?

• A. They are configurational isomers.
• B. They are diastereomers
• C. The cis-isomer has higher dipole moment than the trans-isomer.
• D. The cis isomer usually has a lower boiling point than the trans-isomer.

Answer 1

The correct option is D The cis isomer usually has a lower boiling point than the trans-isomer.

Trans has no (or zero) dipole moment tha 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, and hence cis isomer is more polar than trans. While trans is more symmetric in nature, so it can be more closely packed. So, it has a higher melting point.
Molecules with higher dipole moments have larger intermolecular forces of attraction due to this large amount of heat is required to overcome the intermolecular forces and So, boiling point also increases.