Is the Fourier Transform Infrared Free-OH Band of t-Butanol Only from Free OHs? Case Studies on the Binary Systems of the Alcohol with CCl₄ and CHCl₃

Abstract

Attenuated total reflection−Fourier transform infrared spectroscopy and quantum chemical calculations were performed on tert-butyl alcohol (t-BuOH) and its binary solutions with CCl 4 and CHCl 3 . The study was focused on the free-OH stretching bands. Two resolution-enhancing methods, excess spectroscopy and two-dimensional correlation spectroscopy, were employed to examine the structural heterogeneity and search for the detailed contributors to the free-OH bands. Unexpectedly, CCl 4 was found not to be an inert solvent and, similar to CHCl 3 , formed hydrogen/halogen bonds (H-/X-bond) with t-BuOH. It was observed that the free-OH band in the t-BuOH−CHCl 3 system is larger and more red-shifted than that in the t-BuOH− CCl 4 system, indicating the stronger intermolecular interactions in the former system. Furthermore, in the t-BuOH−CHCl 3 system, the H-bonds are stronger than the X-bonds, while in the t-BuOH− CCl 4 system, both interactions are similar in strength. To assign the free-OH bands, it was found that they are not only from the free OH of the t-BuOH monomer, but they are also contributed by the quasi-free OH with the oxygen bonded to H or Cl and even the weakly H-bonded OH of t-BuOH molecules. Finally, all the identified species increased simultaneously via cosolvent addition, suggestive of the destabilization of the highly associated t-BuOH clusters.

The Structures of ZnCl2-Ethanol Mixtures, a Spectroscopic and Quantum Chemical Calculation Study

“…The H-bonded networks in alcohols are readily susceptible to disruption and reformation by chemical perturbations [ 9 , 10 , 11 ]. Structural properties of alcohols in pure state or mixed with cosolvents and their relationship with H-bonds have been the subject of numerous experimental and computational studies [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. When it comes to electrolytes, their solvation in alcohols and aqueous alcohol solutions are of great significance in many industrial and natural processes [ 22 , 23 , 24 ].…”

“…These scarcities encouraged us to undertake the present work where attenuated total reflection Fourier transform infrared (ATR-FTIR) and quantum chemical calculations including Hirshfeld charge analysis have been used to study the spectral behavior and quantum chemical properties of a wide range of compositions of ZnCl 2 -EtOH mixtures. Excess absorption spectroscopy [ 10 , 20 , 58 , 59 ] and two-dimensional correlation spectroscopy (2D-COS) [ 60 ] were particularly utilized to enhance the resolution of the overlapped initial IR bands. Acquiring this molecular-level knowledge would help qualitatively rationalize the observed macroscopic properties such as vapor pressure of similar mixtures.…”

Generalized Excess Spectroscopy

“…Finally, to check whether the equipment works normally and the data processing is correct, we suggest taking the binary liquid system t-BuOH−CCl 4 as the standard system and compare the obtained excess spectra in the midinfrared region with the literature results. 14,28 6. CONCLUDING REMARKS In this work, we proposed generalized excess spectroscopy, an extended method to construct the ideal spectra with the spectra of the mixtures instead of those of the pure compounds.…”

“…At present, we recommend to do the job with the assistance of quantum chemical calculations. 23,[26][27][28][30][31][32]34 ■ ASSOCIATED CONTENT * sı Supporting Information…”

“…Particularly for IR, this method is widely suitable, regardless of the near-infrared, mid-infrared, or far-infrared range. In recent years, abundant interesting results of solution structures and molecular interactions have been obtained by employing the excess IR spectroscopy approach. ,,− …”