Octanol/water partition coefficient of ortho-substituted aromatic solutes.

The partition coefficient (P) of some mono- and di-ortho-substituted aromatic compounds was measured in a 1-octanol/water system. For each series of compounds with the same functional group, the pi value (the difference in the log P value between the substituted and unsubstituted compound) was analyzed on the same basis as the values of meta- and para-substituted isomers by an extended Hammett-Taft procedure. In the procedure, we considered the intramolecular electronic and steric effects, operating between substituents and governing the relative hydrogen-bonding solvation with partitioning solvents for solutes in which internal hydrogen-bond formation can be ignored. The pi value for mono- and di-ortho-substituted derivatives was adequately included in the correlation equation for the values of the meta- and para-substituted derivatives in each series. The effect of di-ortho substituents on partition behaviors could be roughly expressed by the sum of the effects of the 2- and 6-position substituents.