Hansch-Leo fragment method

Laboratory measurements of and S, can be costly and difficult. Various methods, including group contribution technique and quantitative structure (or property) property relationships (QSPRs or QPPRs), are available to estimate and S., from which o values can be derived. A direct approach of predicting o has also been established based on the dependence of cosolvency on solute hydrophobicity. Among a number of polarity indices, octanol/water partition coefficient, was initially chosen by Yalkowsky and Roseman for correlation with o, due mainly to the abundance of available experimental data and the wide acceptance of the Hansch-Leo fragment method for its estimation. is a macroscopic property which does not necessarily correlate with microscale polarity indices such as dipole moment, and only in a rank order correlates with other macroscopic polarity indicators such as surface tension, relative permittivity, and solubility parameter. 

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