In the following pairs, which gas the higher boiling point: #cis#- or #trans#-but-2-ene; #cis#- or #trans#-1,2-dichloroethene?
1 Answer
Sep 17, 2017
Usually, the cis isomer has stronger intermolecular forces.
Explanation:
For example, the
Each
Molecules with a net dipole will have stronger intermolecular dipole-dipole attractions than molecules with no net dipole..
The dipole moment of trans-but-2-ene is zero, because the bond dipoles cancel.
However, the dipole moment of cis-but-2-ene is 0.33 D, the vector sum of the two bond dipoles.
Similarly, cis-1,2-dichloroethene has a high dipole moment, but that of trans-1,2-dichloroethene is zero.
In each case, the molecule with the higher dipole-dipole attractions has the higher boiling point.