Question

Which is correct regarding the boiling point of the following compounds:

cis trans

• A. Boiling point of cis isomer is more than the trans isomer
• B. Boiling point of trans isomer is more than the cis isomer
• C. Both cis and trans isomers will have equal boiling point
• D. None of these

Answer 1

The correct option is A Boiling point of cis isomer is more than the trans isomer

In the cis isomer, the terminal groups are on the same side of the double bond. Hence, the cis isomer has a resultant dipole moment. Whereas, in the trans isomer, the terminal groups on the opposite sides of the double bond cancel the dipole moment and have zero net dipole moment.
Therefore, the molecules with higher dipole moments have larger intermolecular forces of attraction, and a large amount of heat is required to overcome the intermolecular forces. So, the boiling point also increases.
Hence, the cis isomer is polar in nature and has a higher boiling point as compared to that of the trans isomer.