Effects of charge and intramolecular structure on the lipophilicity of nitrophenols

The lipophilicity of a series of phenolic compounds was studied in the 1,2- dichloroethane (1,2-DCE)/water system. Cyclic voltammetry at the ITIES was used to study the transfer characteristics of the charged species, and thei r partition coefficient was deduced from their formal transfer potential. F or the neutral species, log P-DCE values were measured by a two-phase pi-I- metric method. The results are compared to those previously obtained in oct anol/water and by linear solvation energy relationships (LSER) in the two s olvent systems. It is shown that nitrophenols with intramolecular II-bondin g deviate from the solvatochromic equation for the 1,2-DCE/water system, an d discrepancies between both approaches are discussed on the basis of confo rmational and steric effects. When charged however, all the species have ap proximately the same partition coefficients because the effect of the intra molecular H-bond disappears and the differences in measured lipophilicity a rise from the variation of the intramolecular charge delocalization due to resonance equilibria. Some biological implications of these properties are discussed.