Polar and Nonpolar Interactions Encoded in Lipophilicity

The parameter A, being a global measure of a solute s polarity, should by definition contain the same information as Eq. [2] or [3] except for the volume term. This has been confirmed for octanoi/water (Eq. [6]) and alkane/water (Eq. [7]) partition coefficients  

These equations make explicit the individual polar terms that are negatively related to lipophilicity and account for most polar interactions between a solute and the two solvent phases. In the case of the octanoi/water system (Eq. [6]), the main contributor to a solute s polarity is thus its H-bond acceptor basicity 0), and to a lesser extent its dipolarity/ polarizability (ir ). In contrast, the polar interactions expressed in alkane/ water partition coefficients (Eq. [7]) are the H-bond donor acidity (a) and the H-bond acceptor basicity 0), and again to a lesser extent the dipolarity/polarizability (ir ). 

The steric term used in factorizing lipophilicity can be defined as a descriptor of the solute s capacity to enter nonpolar interactions with the aqueous and organic phases (i.e., hydrophobic interactions and dispersion forces). Whether cavity formation also plays a role is debatable and will not be discussed here. To simplify the vocabulary in this chapter, it is convenient to equate hydrophobicity with the nonpolar interactions encoded by the steric term. In this nomenclature, hydrophobidty is not synonymous with lipophilicity, but a mere component of it. 

the conclusion emerges that lipophilicity can find a general and qualitative expression as follows  

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