5.1.2 Dipole-dipole forces
In the case of dipole-dipole interactions, the molecules that bond together have a fixed asymmetry in their charge distributions (as is the case in Figure 22); if their orientations are favourable the two will bond together. All molecules produce London forces. The dipole-dipole interactions are in addition to these and are, perhaps surprisingly, usually much weaker.
There are many everyday examples of these bonds. For instance, they are to be found between molecules in liquids. A liquid is a loose association of its constituent atoms or molecules; not so loose that they fly apart, but they are easily separated by, for example, heat or gravitational forces.
What distinguishes dipole–dipole forces from London forces?
Dipole–dipole interactions are independent of time. London forces do not have a permanent static-charge distribution.