The temperature-induced changes in hydrogen bonding of decan-1-ol in the pure liquid phase studied by two-dimensional Fourier transform near-infraredcorrelation spectroscopy

Fourier transform near-infrared (FT-NIR) spectra of decan-1-ol in the pure liquid phase were investigated in the regions of the first and second overt ones of the OH stretching vibration over the temperature range 15-76 degree s C. The dynamics of temperature-induced changes in the hydrogen bonding we re explored by the 2D correlation approach. It was found that the first ove rtone of the monomer band is split into two peaks (7087 and 7114 cm(-1)). T he peaks originate from the rotational isomerism of the OH group. Although the trans-isomer (at 7114 Cm-1) is more stable than the gauche-isomer (at 7 087 cm(-1)), the intensity of the band due to the former is weaker in the p ure liquid phase. In dilute solutions the situation is reversed. This effec t can be explained by higher accessibility of the OH proton in the trans-po sition, Therefore, the population of the free protons in the trans-position is reduced faster with increase in concentration. The band attributed to t he free terminal OH groups in open chain polymers was not observed in the 2 D correlation spectra of neat decan-1-ol. As for butanols, studied previous ly, the populations of the polymers and cyclic dimers vary faster than that of the monomers. When the temperature is raised, the population of the mon omers increases faster where that of the polymers decreases more slowly. He nce it is concluded that the growth in the population of the monomeric spec ies comes from dissociation of the intermediate species. These 2D correlati on studies on alcohols in the pure liquid state suggest that the degree of association in the saturated straight-chain alcohols decreases with increas e in chain length.