Breaking the Structure of Liquid Hydrogenated Alcohols Using Perfluorinated tert-Butanol: A Multitechnique Approach (Infrared, Raman, and X-ray Scattering) Analyzed by DFT and Molecular Dynamics Calculations

Abstract

The state of aggregation at room temperature of tert-butanol (TBH) and perfluoro tert-butanol (TBF) liquid mixtures is assessed by vibrational spectroscopy (Raman and infrared) and X-ray diffraction and analyzed using density functional theory (DFT) and molecular dynamics (MD) simulations. It is shown that larger clusters (mostly tetramers) of TBH are destroyed upon dilution with TBF. Small oligomers, monomers, and mainly heterodimers are present at the equimolar concentration. At variance with slightly interacting solvents, the signature of hetero-oligomers is shown by the appearance of a new broad band detected in the infrared region. The same spectral observation is detected for mixtures of other hydrogenated alcohols (methanol and 1-butanol). The new infrared feature is unaffected by dilution in a polar solvent (CDCl 3 ) in a high-concentration domain, allowing us to assign it to the signature of small hetero-oligomers. MD simulations are used to assess the nature of the species present in the mixture (monomers and small hetero-oligomers) and to follow the evolution of their population upon the dilution. Combining MD simulations with DFT calculations, the infrared spectral profile is successfully analyzed in equimolecular mixtures. This study shows that TBF is a structure breaker of hydrogen-bonded alcohol networks and that the TBF (donor)−TBH (acceptor) heterodimer is the dominant species in an extended range of concentration, centered in the vicinity of the equimolar fraction.

The path towards type V deep eutectic solvents: inductive effects and steric hindrance in the system tert-butanol + perfluoro tert-butanol

“…It is not surprising that the stoichiometries of solids α and β are the most common aggregation states observed in the liquid mixtures; the hetero-dimer TBH–TBF and the trimer TBH–TBF–TBH. 30 The formation of stoichiometric compounds could be mitigated by decreasing the extent of fluorination and further decreasing the melting temperature of eutectic mixtures.…”

“…The perfluorinated compound TBF, which in its pure liquid phase is mostly found as isolated monomers, is able to form a very strong hydrogen bond in the presence of TBH. 30 Due to the lower ability of TBF to associate in the pure form, which can be attributed to the steric hindrance and inductive effects created by the -CF 3 substituents, the magnitude of the excess molar enthalpy is comparable to the energy of a single hydrogen bond. As such, the very The MD simulations, using the original charge distributions, are able to reproduce the sign, shape and order of magnitude of the H E curve, predicting a value that is around 50% of the experimental for the equimolar composition.…”

“…It is not surprising that the stoichiometries of solids a and b are the most common aggregation states observed in the liquid mixtures; the heterodimer TBH-TBF and the trimer TBH-TBF-TBH. 30 The formation of stoichiometric compounds could be mitigated by decreasing the extent of fluorination and further decreasing the melting temperature of eutectic mixtures. The expanded uncertainties of the experimental results, including the calibration uncertainty, were assigned based on independent experiments as t  s= ffiffi ffi n p , where t is obtained from Student's t-distribution (0.95 level of confidence), s is the standard deviation and n is the number of independent experiments.…”

“…The behaviour of TBF as an asymmetric HBD is further supported by previous studies of the liquid phase of mixtures of TBF-TBH (note the resemblance between TBF-TBH and thymol-menthol). 29,30 Using a variety of techniques including vibrational spectroscopy (Raman and infrared) and X-ray diffraction, supported by DFT and MD simulations, it was possible to show that TBF acts as a structure breaker of TBH alcohol networks and that the 1 : 1 TBF-TBH hetero-dimer is the dominant species in the mole fraction concentration range of 0.3-0.7. For mixtures richer in TBF the characteristic monomers of the pure TBF liquid phase become dominant, while for mixtures richer in TBH oligomers start to appear with some relevance of the 2 : 1 trimer TBH-TBF-TBH.…”

Perfluorinated Alcohols at High Pressure: Experimental Liquid Density and Computer Simulations

“…Mixtures of fluorinated and hydrogenated alcohols have also been studied in both the liquid and gaseous phases. − These mixtures display a very complex behavior when compared with mixtures of hydrogenated alcohols. For example, excess volumes are large and positive, whereas those of mixtures of hydrogenated alcohols are practically zero .…”