Relationship between molar refraction and n-octanol/water partition coefficient.

The n-octanol/water partition coefficient (Pow) for organic chemicals which do not form the hydrogen bond was considered on the basis of London's dispersion force, because the dispersion force is the main component of van der Waals-type attractive forces between solute and solvent molecules. The dispersion force is a function of both the ionization potential and the molar refraction. As the variation of the ionization potential is small in comparison with that of the molar refraction, the latter is the most important factor to determine the value of Pow. Thus the relationship between Pow and the molar refraction can be established. The relationship was confirmed for some halogenated alkanes, alkenes and aromatics, and polycyclic aromatic hydrocarbons by analysis of observed values of Pow and calculated values of the molar refraction. Estimation of Pow from the molar refraction is advantageous for the preliminary hazard assessment of new chemicals, because direct measurement of Pow is laborious and time consuming for lack of information about analytical methods.