Alkenes: Physical Properties
The physical properties of alkenes are very similar to those of alkanes. Alkenes also exist as gases, liquids, and solids at room temperature. Isomeric alkenes tend to have similar boiling points, which makes it difficult to separate them by boiling point differences.
Substituted alkenes show small dipole moments due to small electron distribution differences. These small differences allow cis and trans isomers to be distinguished from each other. The effects of substitution must be deduced for each molecule, based on the positions and the electronegativity of the atoms or groups attached to the carbon‐carbon double bond. Thus, in the case of cis‐ and trans‐2‐butene, the cis isomer shows a dipole moment of 0.33 debye units (D), while the trans isomer shows a dipole moment of 0 D, due to cancellation of the electronic effects.