Question 10.2: 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.
STRATEGY
First, use the VSEPR model described in Section 7.9 to predict the molecular shape of vinyl chloride. Then, assign polarities to the individual bonds according to the differences in electronegativity of the bonded atoms (Figure 7.4 on page 221), and make a reasonable guess about the overall polarity that would result by summing the individual contributions.
Because both carbon atoms have three charge clouds, each has trigonal planar geometry and the molecule as a whole is planar:
Vinyl chloride \begin{matrix} H\ \ \ \ \ \ \ \ \ \ \ \ H\\^{^{\diagdown }}_{_{\diagup }}C=C^{^{\diagup }}_{_{\diagdown }}\\H\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ H \end{matrix} 
Top view Side view
Only the C–Cl bond has a substantial polarity, giving the molecule a net polarity:
