FT-IR spectroscopic investigations of hydrogen bonding in alcohol–hydrocarbon solutions

As part of a project on thermodynamic properties of H-bonding solutions, Fourier-transformed infrared (FT-IR) spectroscopic investigations of 14 binary systems of the type (alcohol or phenol)+hydrocarbon were carried out at temperatures of 283, 298 and 313 K. The alcohols were primary alcohols (1-alkanols from C1 to C6), secondary alcohols (2-propanol and cyclohexanol) and a tertiary alcohol (2-methyl-2-propanol), the solvents were n-hexane and cyclohexane. FT-IR spectroscopy provides quantitative information on the distribution of the alcohol molecules to the monomer and H-bonded species, respectively. Furthermore, direct evidence on the type of H-bonded species is obtained. For the data evaluation, H-bonding is described by a thermodynamically consistent chemical theory, which takes into account the monomer, dimer and one typical representative of the higher oligomers (UNIQUAC 1-2-n association model). In addition to the FT-IR data, NMR data have been taken for the system 1-butanol+cyclohexane, primarily to test the infrared (IR) spectroscopic results. Good agreement was observed. The large number of systems studied in the present work allows to obtain quantitative information on the influence of the shape and the size of both the alcohols and the solvents on H-bonding. The results provide a large data base for the development of thermodynamic models of H-bonding solutions.