SELF-ASSOCIATION OF CYCLOHEXANOLS IN INERT SOLVENTS - APPARENT HEAT-CAPACITIES OF CYCLOHEXANOL AND SUBSTITUTED CYCLOHEXANOLS IN NORMAL-HEPTANE AND NORMAL-DECANE

Apparent heat capacities have been measured for cyclohexanol and substituted cyclohexanols in dilute n-heptane and n-decane at 25-degrees-C. The alcohols are cyclohexanol, 2-ethylcyclohexanol, 2-tert-butylcyclohexanol, trans-2-phenylcyclohexanol, 2,6-dimethylcyclohexanol, 2,3-dimethylcyclohexanol, 3,4-dimethylcyclohexanol, 3,3,5-trimethylcyclohexanol and 3,3,5,5-tetramethylcyclohexanol. The associational part of the apparent molar heat capacity, phi-c(assoc), shows a maximum against concentration which decreases and moves to higher alcohol concentration as the hydroxyl group on the alcohol becomes increasingly hindered, effectively reducing the self-association capability. A comparison between cyclohexanols and the previously reported phenols (J. Chem. Soc., Faraday Trans., 1991, 87, 1733) indicates that cyclohexanols show a higher ability to self-associate owing to the larger flexibility of the cyclohexanol ring as compared to the rigid aromatic ring. Treszczanowicz-Kehiaian theory for associated liquids was used to obtain the volumetric equilibrium constants and the enthalpy change for the formation of hydrogen bonds, DELTA-H0. For cyclohexanols DELTA-H0 is higher than for the corresponding phenols. As with the phenols, the tetramer population is severely reduced, dimers and trimers being more important.