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Thermodynamics of Water-octanol and Water-cyclohexane Partitioning of some Aromatic Compounds
School of Pharmacy and Chemistry, Liverpool John Moores University, Byrom Street, Liverpool L 3 3AF, UK
* Author to whom correspondence should be addressed.
Received: 4 August 2004; in revised form: 3 February 2005 / Accepted: 3 February 2005 / Published: 31 January 2005
Abstract: The Gibbs free energy, enthalpy and entropy of partitioning of 45 simple aromatic compounds (phenols, benzoic acids and acetanilides) from water to octanol and from water to cyclohexane have been determined using the filter-probe method. This involved the measurement of partition coefficients over the temperature range 20-45oC. The aim of the work was to explore the effects of intramolecular hydrogen bonding and steric factors on the partitioning process. It was found that the intramolecular hydrogen bond is intact in 2-nitrophenol and salicylic acid, and possibly in 2-hydroxybenzaldehyde, in all three solvents, but 2-chlorophenol is intramolecularly hydrogen bonded only in inert solution. The evidence indicates that 2-nitroresorcinol and 2,6-dihydroxybenzoic acid possess only one intramolecular hydrogen bond, although they are theoretically capable of possessing two. There is evidence of steric shielding in 2,6-dimethylphenol, whilst 2,6-dimethylbenzoic acid and ortho-substituted acetanilides show evidence of steric twisting of the carboxyl and acetamido groups respectively out of the plane of the aromatic ring. Unusual steric effects are displayed in the methyl-2-nitrophenols whereby, depending upon the position of the methyl group, the intramolecular hydrogen bond is either weakened or strengthened.
Keywords: Partition coefficient; thermodynamics of partitioning; intramolecular hydrogen bond; steric effect
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Dearden, J.C.; Bresnen, G.M. Thermodynamics of Water-octanol and Water-cyclohexane Partitioning of some Aromatic Compounds. Int. J. Mol. Sci. 2005, 6, 119-129.
Dearden JC, Bresnen GM. Thermodynamics of Water-octanol and Water-cyclohexane Partitioning of some Aromatic Compounds. International Journal of Molecular Sciences. 2005; 6(1):119-129.
Dearden, J. C.; Bresnen, G. M. 2005. "Thermodynamics of Water-octanol and Water-cyclohexane Partitioning of some Aromatic Compounds." Int. J. Mol. Sci. 6, no. 1: 119-129.