Polarity

Alkenes are relatively nonpolar. They are insoluble in water, but soluble in nonpolar solvents such as hexane. Alkenes are slightly more polar than alkanes for two reasons: the pi bond electrons are more polarizable, thus contributing to instantaneous dipole moments, and the vinylic bond tends to be slightly polar, contributing to the permanent dipole moment.

In a symmetrical trans disubstituted alkene, the sum of the dipole moments is zero. In the analogous cis alkene, the vector sum of the two dipoles is directed perpendicular to the double bond. This results in a non-zero molecular dipole. The permanent dipole results in an increased bp.

In a symmetrical trans disubstituted alkene, the sum of the dipole moments is zero. In the analogous cis alkene, the vector sum of the two dipoles is directed perpendicular to the double bond. This results in a non-zero molecular dipole. The permanent dipole results in an increased bp.