Question 8.6: Predicting the Presence of a Dipole Moment Would you expect ...
Predicting the Presence of a Dipole Moment
Would you expect vinyl chloride (H_{2}C=CHCl), the starting material used for preparation of poly(vinyl chloride) polymer, to have a dipole moment? If so, indicate the direction
Follow the procedure outlined in Figure 8.8 for determining molecular polarity. The electron-dot structure for vinyl chloride is:
Then use the VSEPR model described in Section 8.1 to predict the molecular shape of vinyl chloride. Each carbon has trigonal planar geometry because both carbon atoms have three charge clouds. The molecule as a whole is planar because the unhybridized carbon 2p orbitals in the pi part of the C=C double bond overlap in a sideways manner:
Then assign polarities to the individual bonds according to the differences in electronegativity of the bonded atoms, and make a reasonable guess about the overall polarity that would result by evaluating symmetry in bond dipoles and summing the individual contributions. Only the C-Cl bond has a substantial polarity, giving the molecule a net polarity in the direction of the chlorine atom:
