Another example, this time of internal electrical compensation is the low dipole moment of dioxane, (quoted by some as 0.45 debyes others as close to zero). Dioxane is miscible with water and therefore strongly polar. Comparing dioxane with diethyl ether which has a dipole moment of 1.15 debyes (which one would deduce should be less than that of dioxane as it is only slightly soluble in water) it would seem that the strong internal compensation between the dipoles from each of the ether groups reduces the overall dipole moment of dioxane to something less than one might expect. However, another molecule, approaching one ether group of the dioxane molecule would experience the uncompensated field of that single dipole and again interact accordingly.

Figure 31. Polar Interactions: Dipole-Dipole Interactions

Thus, the polarizability of a substance containing no dipoles may well give an indication of the strength of the dispersive interactions that might take place with another molecule. In contrast, due to possible self-association or internal compensation, the dipole moment of a substance, determined from bulk dielectric constant measurements, may not always give an indication of the strength of any polar interaction with another molecule. A diagrammatic impression of a dipole-dipole interaction is shown in figure 31. The dipoles interact directly as would be expected, but it is important to appreciate that behind the dipole-dipole interaction is the dispersive interaction from the charge fluctuations on both molecules. The net molecular interaction will, therefore, be a combination of both. Examples of some substances that have permanent dipoles and exhibit polar interaction with other molecules are alcohols, esters, ethers, amines, amides, nitriles, etc.