Infrared spectra and conformational analysis of anti and gauche deuterated ethanol isotopomers

Abstract

The infrared spectra of dilute CCl 4 solutions of deuterated ethanol isotopomers have been examined in the fundamental OH/OD stretching absorption regions. The compounds studied are comprised of undeuterated CH 3CH 2OH, and four deuterated isomers, CH 3CD 2OH, CD 3CH 2OH, CH 3CH 2OD, and CD 3CD 2OD. Doublet character of the high energy IR hydroxy band, indicating the existence of anti and gauche conformational isomers, is found for each isotopomer in agreement with previous IR studies of primary saturated alkanols. A variable temperature study of the deconvoluted spectra for the undeuterated ethanol system provides a reference experimental estimate of the relative enthalpies of the C s (anti) and C 1 (gauche) conformers. The analysis also allows a determination of the intensities of the individual bands. Spectral and thermodynamic results from HF/6-311++G* calculations are compared with the experimental observations. The deconvoluted spectra for the deuterated isomers are compared to the ethanol results, and small differences in OH absorption band frequencies are observed. The equilibrium constants for gauche to anti conversion for two OD compounds are somewhat larger than those for the three OH isomers.