Moment, Polarity, and Polarizability

The dissolution behavior of a solvent cannot be predicted solely on the basis of its dipole moment. For example, dioxane (/t = 0.4 D) is a very good solvent and has a comparable solvency to dimethyl sulfoxide (/t = 4.0 D). 

Dipole-dipole and induction forces in solvents or solutions decrease with increasing molecular mass of the solvent [14.43]. Since this effect is not reflected in the dipole moment of the solvent, a polarizability parameter P is used to describe the dipole dipole interaction forces [14.34]. This parameter can be calculated from the ionization potential IP, polarizability a, and dipole moment fi [14.44]  

The dipole moment /i is also used in conjunction with the solubility parameter S as a coordinate in solubility diagrams to take account of the influence of variations in polarity [14.44]-[14.46]. 

The polarizability a of an electrically neutral compound is a measure of the displaceability of charge carriers within the molecule. The greater the polarizability, the stronger are the dipoles induced by an external electromagnetic field the magnitude of the polarizability and strength of the dispersion forces are thus related to one another. 

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