Effect of Intramolecular Hydrogen Bonding on Partition Coefficients
DEFENCE RESEARCH ESTABLISHMENT SUFFIELD RALSTON (ALBERTA)
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Hansch favours the use of 1-octanol-water for partitioning organic compounds. The advantage ascribed to this and other alcohol-water systems is that the same equation serves to calculate log Palc-water values for compounds with and without intermolecular hydrogen bonding. Hansch and others have attempted, without much success, to develop equations for calculating the effect of intermolecular hydrogen bonding upon partition coefficients determined in hydrocarbonwater systems. In this paper, attention is directed towards a similar study of phenols with a functional group at C2 or C4. Using conjugative effects, millimicron units, and steric effects, millimicron units, developed for calculating long-wavelength U.V. absorption maxima of the conjugated heteroenoid compounds, permitted the development of equations relating log P in the system cyclohexane-water and log P in the system 1-octanol-water for 2-hydroxy- derivatives to those for the respective isomers with the hydroxyl at C4. Incorporation of pKA into equations analogous to those above related log Ppara and log Ppara for the 4-hydroxy derivatives respectively to log PH and log PH for the parent compounds. Addition of the appropriate equations from the above two sets permits the calculation of log Portho values for 2-hydroxy derivatives in the system cyclohexane-water, where intramolecular hydrogen bonding occurs, from log PH values. Methods for calculating log PH and log PH values have already been outlined.
- Organic Chemistry
- Atomic and Molecular Physics and Spectroscopy