Identification of alcohol conformers by Raman spectra in the C-H stretching region

J Phys Chem A. 2015 Apr 2;119(13):3209-17. doi: 10.1021/jp513027r. Epub 2015 Mar 20.

Abstract

The spontaneous polarized Raman spectra of normal and deuterated alcohols (C2-C5) have been recorded in the C-H stretching region. In the isotropic Raman spectra, a doublet of -CαH stretching vibration is found for all alcohols at below 2900 cm(-1) and above 2950 cm(-1). By comparing the experimental and calculated spectra of various deuterated alcohols, the doublets are attributed to the -CαH stretching vibration of different conformers. For ethanol, the band observed at 2970 cm(-1) is assigned as the stretching vibration of -CαH in the Cα-O-H plane of the gauche-conformer, while the band at 2895 cm(-1) is contributed from both the -CαH2 symmetrical stretching vibration of the trans-conformer and the -CαH stretching vibration out of the Cα-O-H plane of the gauche-conformer. The population of gauche-conformer is estimated to be 54% in liquid ethanol. For the larger alcohols, the same assignments for the doublet are obtained, and the populations of gauche-conformers with plane carbon skeleton are found to be slightly larger than that of ethanol, which is consistent with results from molecular dynamics simulations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1-Propanol / chemistry*
  • Deuterium
  • Ethanol / chemistry*
  • Hydrogen Bonding
  • Software
  • Spectrum Analysis, Raman / methods*

Substances

  • Ethanol
  • 1-Propanol
  • Deuterium