Question

Why does cis but 2 ene has lower melting point than trans but 2 ene?

Answer 1

In the cis isomer, both the bulky groups are present on the same side as shown in the above fig. , hence it has a dipole moment, (which gets cancelled out in case of trans). Thus, cis-But-2-ene has a higher dipole moment due to which it is more ionic, hence higher boiling point.