Octanol/water partition coefficients Kow: A critical examination of the value of the methylene group contribution to log Kow for homologous series of organic compounds

摘要: Abstract The literature data for the values of octanol/water partition coefficient KOW are examined critically, specifically in relation to methylene group increment log KOW – here called lipicity L homologous series. With simply substituted alkanes, plots versus number m linear, following form: L = α + βm (Collander equation). slope parameter β represents increment, which widely is expected be constant on simplest theoretical grounds, and assumed so most practical applications. Collander equation behaviour some 84 series subseries, ranging complexity from alkanes up alkyladenines alkyl galactosides, presented graphically. Compounds with α,ω-disubstituted chains give nonlinear plots. remaining linear plots, but not constant, variation being statistically significant, distribution essentially normal (Gaussian) mean value ¯ = 0.52 standard deviation σ(β) = 0.06. other solvent/water systems ethoxyethane (diethyl ether), two heptane hexadecane show similar behaviour. Most significantly, fact that casts doubts applicability free energy approach, “fragmental methods” used interpreting predicting coefficients. More generally, graphical approach essential a proper treatment correlations this kind; graphs form an atlas shows at glance these series, revealing anomalies need rectified, gaps filled.