Two-dimensional FT-NIR correlation study of hydrogen bonding in the butan-1-ol/water system

The effects of temperature and concentration on hydrogen bonding in butan-1-ol/water binary mixtures have been studied by using generalized 2D Fourier transform (FT) near-infrared (NIR) correlation spectroscopy. Particular attention has been paid to the analysis of changes in the self-association of butan-1-ol resulting from the presence of water. The obtained results indicate that the -self-association of butan-1-ol is not influenced by small additions of water. When the molar fraction of water (X-H2O) increases, bands due to water appear in the spectra. The number of correlation peaks suggests the presence of two different species of hydrogen-bonded water. In addition, molecules of non-hydrogen-bonded water dispersed among molecules of butan-1-ol were detected. An increase in X-H2O at constant temperature reduces the population of the polymeric species of butan-1-ol and leads to growth in the number of free OH groups. When X-H2O increases further, the free OH groups of butan-1-ol interact with molecules of water. The asynchronous peak originating from the rotational isomerism of butan-1-ol disappears from the spectra of the mixtures with higher values of X-H2O. This observation indicates that the molecules of water do not reveal conformational selectivity upon the formation of hydrogen bonds with molecules of butan-1-ol. In contrast, due to larger molecular size, this selectivity appears for butan-1-ol. Both the temperature- and concentration-dependent correlation spectra provide evidence that in the studied system water-water and alcohol-alcohol interactions dominate, whereas the water-alcohol interactions are weaker.