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

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.