Vapour phase infrared studies of alcohols - I. Intramolecular interactions and self-association

Abstract

Infrared spectra are reported of methanol, ethanol, propan-2-ol, 2-methylpropan-2-ol, 2, 2, 2-trifluoroethanol, 2, 2, 3, 3-tetrafluoropropan-1-ol and 1, 1, 1, 3, 3, 3-hexafluoropropan-2-ol in the vapour phase in a 1 m path-length cell at pressures up to the s. v. p. of the alcohol. Also reported are 40 m path-length vapour and argon matrix spectra of trifluoroethanol. Dimer absorptions are identified for all the alkanols and for trifluoroethanol, and some estimates of ∆ H provided. Trifluoroethanol exhibits a striking series of sum-and-difference bands of the OH stretch with other fundamentals, 14 summation modes being observed extending in frequency to over 5000 cm -1 and involving most of the fundamentals below 1500 cm -1 . Other fluoroalcohols with fluorines substituted on β carbon atoms exhibit similar sum-and-difference modes. The alkanols exhibit only one such pair of bands due to the OH stretch plus or minus the OH torsion, and this provides a convenient method of measuring the torsional frequencies. The different behaviour of the fluoroalcohols is attributed to intramolecular hydrogen bonding.