Association of 1-Hexanol (cas 111-27-3) in mixtures with n-hexane: Dielectric, near-infrared and DFT studies

Add time:08/21/2019    Source:sciencedirect.com

Association of 1-Hexanol (cas 111-27-3) in n-hexane has been studied by measurements of nonlinear dielectric effect (NDE) and near-infrared (NIR) spectroscopy. Besides, the dipole moments of selected open and cyclic associates were determined by DFT (density functional theory) calculations. All measurements were performed in the whole range of mole fractions with a step of 0.1. From numerical fitting of the dielectric data we obtained populations of all species present in the mixture. Our results do not support common opinion about the exceptional role of cyclic tetramers. The most abundant cyclic species are trimers and population of the cyclic associates rapidly decreases with increasing size of associates. The variations in population of open associates are more complex and for mole fractions of 1-hexanol > 0.1 the relationships have a maximum, which shifts towards higher associates. In pure 1-hexanol this maximum is close to seven. From analysis of the dielectric data it results that at lower alcohol content dominate the cyclic species. When the concentration of 1-hexanol increases the equilibrium shifts towards formation of the linear associates.From NIR spectra we determined the overall population of the free OH in monomers and open associates. Next, these values were used for estimation of an average length of the open associates. It appears that an averaged size of the open associates determined from NIR spectra is higher than that from the dielectric data and these differences are more pronounced when the concentration of 1-hexanol increases. We discuss possible explanations of this observation. Assuming that the actual size of the open associates is between those obtained from both methods, one can estimate that the size of open associates is ranging from 3 to 15 in pure 1-hexanol. It seems that the higher associates are stabilized by interaction of the aliphatic chains.

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