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

The infrared spectra of dilute CCl4 solutions of deuterated ethanol isotopomers have been examined in the fundamental OH/OD stretching absorption regions. The compounds studied are comprised of undeuterated CH3CH2OH, and four deuterated isomers, CH3CD2OH, CD3CH2OH, CH3CH2OD, and CD3CD2OD. 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 Cs (anti) and C1 (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.