Partition additive constitutive parameter

One of the most important contributions of Hansch was the discovery that partition coefficients are additive constitutive parameters, like some other molecular properties. He defined a lipophilidty parameter k (eq. 29) [15, 17, 18, 174, 218, 237, 238] in the manner that Hammett a constants (eq. 3, chapter 1.1) were defined. 

BR is the relative biologic activity under investigation, for example the molar EDr>o or the percent response at a given dose. Log P is the logarithm of the octanol-water partition coefficient, a is the approprite Hammett signa constant (electronic in nature), and Es is the Taft steric parameter. With the important demonstration by Hansch that the partition coefficient is often an additive constitutive property, all of the physical parameers may be obtained from the literature. A second important contribution by Hansch is the recognition that the use of statistical techniques is essential to the analysis of quantitative structure-activity relationships. To develop an equation such as that above, one feeds the... 

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