Question 13.9:- 

Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?

Hex-2-ene is represented as: 

                   H3C - HC = CH - CH2 - CH3

Geometrical isomers of hex-2-ene are:


The dipole moment of cis-compound is a sum of the dipole moments of C-CH3 and C-CH2CH3 bonds acting in the same direction.

The dipole moment of trans-compound is the resultant of the dipole moments C-CH3 and C-CH2CH3 of bonds acting in opposite directions.

Hence, cis-isomer is more polar than trans-isomer. The higher the polarity, the greater is the intermolecular dipole-dipole interaction and the higher will be the boiling point.
Hence, cis-isomer will have a higher boiling point than trans-isomer.