Effect of Temperature and Concentration on Self-Association of Octan-1-ol Studied by Two-Dimensional Fourier Transform Near-Infrared Correlation Spectroscopy

Abstract

Temperature- and concentration-dependent variations in self-association of octan-1-ol were studied by two-dimensional (2D) Fourier transform near-infrared (NIR) correlation spectroscopy. The obtained results suggest a similar mechanism of the thermal dissociation of hydrogen-bonded species for octan-1-ol and other straight chain alcohols (butan-1-ol, decan-1-ol). However, the extent of self-association in neat butan-1-ol seems higher than that for longer chain alcohols (octan-1-ol, decan-1-ol) under the same experimental conditions. At low and moderate concentrations of octan-1-ol in CCl4 the dimers are open, while in the pure liquid alcohol one can find some cyclic dimers. In both phases the cyclic aggregates dominate and the amount of the linear species is negligible. The population of the free OH groups increases with temperature, reaching 13% at 80 °C, and this increase occurs faster at elevated temperatures. The synchronous peak near 6600 cm-1 is shown to be a part of the broad polymer band, whereas the feature near 6500 cm-1 was assigned to the νCH + νOH combination mode involving the free OH group. The molar absorptivities of the first and second overtones of the monomer band are similar for various alcohols and do not depend on the solvent. As shown, the second overtone of the monomer band is 20 times less intense than the corresponding first overtone.