The procedure for comparing dipole moments for cis- and trans-alkenes is quite easy, but how to compare dipole moments of

  1. 1,1 dichloroethene (1); and
  2. cis-dichloroethene (2)?

My teacher told me that 1 would have more dipole moment as both chlorines are attached to a single carbon leading to more polarisation of bond, but I was not entirely convinced as the chlorine atoms in 1 would make a $60^\circ$ angle with the horizontal (probably a little larger due to steric repulsions between the two chlorine atoms) whereas the chlorine atoms in 2 would make a only a $30^\circ$ angle with the vertical (where the dipole moment is directed) so 2 should have a greater dipole moment.

Which one is the correct answer? Also is this different for different compounds (e.g., 1,1 diflouroethene or 1,1 diflourobutene etc.)?

  • $\begingroup$ Yes, your reasoning is correct, based on bond angles. Checked the data at CCCBDB! $\endgroup$ – Rahul Verma Aug 6 '20 at 3:26
  • $\begingroup$ Nice website... $\endgroup$ – Manit Agarwal-El psy congroo Aug 6 '20 at 3:37