Question

Arrange the following alkenes in increasing order of their boiling points.

• A. trans-But-2-ene
• B. cis-But-2-ene
• C. trans-Hex-3-ene
• D. cis-Hex-3-ene

Answer 1

With the addition of each -${\mathrm{CH}}_2$ group, the boiling point of alkene increases by $20-30°C$. So Hex-3-ene has higher boiling point.

Trans-alkene has zero dipole moment. Cis- alkene has some dipole moment, thus the compound has some polarity, in turn higher attractions between two molecules.
This results in higher boiling points of cis- alkenes than trans.