Self-association of octan-1-ol in the pure liquid state and in decane solutions as observed by viscosity, self-diffusion, nuclear magnetic resonance and near-infrared spectroscopy measurements
The self-association of octan-1-ol in the pure liquid state and in decane solutions has been studied by near-infrared spectroscopic observation over the temperature range 298.1–348.1 K and also by viscosity, self-diffusion and NMR measurements. The absorption bands assigned to the hydroxy group are superimposed on several bands attributed to the methylene groups belonging to both the alcohol and decane molecules. A superior technique using a computer was adopted for the cancellation of the absorption bands due to the methylene groups so as to obtain the net OH absorption bands. The analysis of the sharp band at 1410 nm (the first overtone band of the OH-stretching vibration attributed to the free OH-monomer and partly to the OH-polymer) leads to the conclusion that the mean degree of association n(i.e. the average size of the multimer in monomeric units) in the polymer of octan-1-ol is ca. four, both in the liquid and in decane solutions under the temperature conditions given above. From the arguments about the aggregated species, a cyclic tetramer was proposed as the associated alcohol species in the liquid and in decane solutions. The association equilibrium constant and other thermodynamic properties such as changes in enthalpy, entropy and Gibbs energy for tetramer formation were also determined.