The models in Table 1 provide some general insight into the factors that affect the accumulation of neutral solutes in the more organic-rich phase, while illustrating the selectivity of biopartitioning processes. System constants with a positive sign favor accumulation of the solute in the organic-rich phase and those with a negative sign favor accumulation in the water-rich phase. The standout feature of the data in Table 1 is that the m system constant is positive and the b system constant is negative for all distribution systems. This is a reflection of the major contribution to biopartitioning from the high cohesion and hydrogen-bond acidity of water. On the other hand, the significant range of numerical values for the m and b system constants is a measure of the cooperative nature of the organic-rich phase in determining solute behavior. This feature confirms our reservations about assigning hydrophobic properties to compounds, but allows the use of the term lipophilicity when applied to a defined distribution process. In the absence of a defined system, the lipophilic character of a compound cannot be determined, because all possible intermolecular interactions are involved in its assessment and the relative importance of individual interactions depends on the complementary properties of the system considered.