Infra-red cryogenic studies. Part 5.—Ethanol and ethanol-d argon matrices

Abstract

Infra-red spectra between 4000 and 40cm-I are reported for EtOH and EtOD suspended in argon matrices at 20 K. The small bandwidths in the low-temperature matrix reveal the presence of bands due to both trans and gauche conformers, and a complete vibrational assignment for the more stable trans conformer is made. The ratio of trans to gauche conformers in the vapour phase at room temperature is estimated to be 2 : 1. Concentration studies result in the identification of open chain dimer, trimer and tetramer, and cyclic tetramer, species from their OH stretching vibrations. The effect of association on other regions of the spectrum is examined.Two conformers of the ethanol molecule may exist, with the OH group trans (I) or gauche (11) with respect to the methyl group :The monomer OH stretching frequency in solution has been reported by some authors as displaying a~ymmetry,l-~ while others report that the band is ~ymmetrical.~ A detailed study of 12 isotopic species from 4000 to 400 cm-l in vapour, liquid and solid phases as well as in solution was inconclusive, the authors tentatively suggesting that the molecule is essentially in the gauche form, on the basis that strong interaction occurs between modes which would be of different symmetry for the trans conformer. However, Michielsen-Effinger reports, from microwave studies, the existence of both trans and gauche conformers of ethanol in the vapour phase, the trans form being the more stable. Takano, Sasada and Satoh6 confirm the existence of a gauche conformer, from similar studies.

Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes

“…23 The far-infrared absorption spectrum of ethanol embedded in cryogenic argon matrices has previously just revealed two strong transitions observed at 211 and 264 cm −1 besides the strong CCO bending fundamental transition at 416.5 cm −1 . 20 In the present far-infrared spectra of ethanol embedded in more inert cryogenic neon matrices, a series of weak, medium-intensity, and strong bands are observed besides the strong CCO bending fundamental transition at 419.9 cm −1 (Fig. 1).…”

A Raman and infrared study of crystalline D-fructose, L-sorbose, and related carbohydrates. Hydrogen bonding and sweetness

“…The band at 3014 cm-' in I (3006 cm-' in 11) is assigned to the antisymmetric v,(CHd mode, and the band at 2895 cm-' in I(2899 cm-I in 11) to the symmetric v,(CH,) mode. In the case of ethanol, the antisymmetric and symmetric CH, stretching modes of the hydroxyniethyl group are observed at 2953 cm-' and at 2900 cm-' , respectively (29).…”

Factor analysis as a complement to band resolution techniques. VI. Complex formation between pentachlorophenol-OD and acetone

“…Several matrix-isolation infrared selfdence of the monomer hydroxyl stretching band only, association studies have shown that hydrogen while the band due to association or complex forma-bonding manifests itself in all three vibrational tion was usually ignored. The application of factor modes of the hydroxyl group in alcohols (6,7). When analysis (principal component analysis) to digitized complex formation occurs between alcohols or infrared spectra leads to the determination of the phenols and ketones, both the v(0H) band and the number of absorbing components in a complex band v(C0) band show concentration dependencies (4).…”

“…[6] instead of the monomeric acceptor concent3aiion. For comparison, P : l equilibriunl constants were also calculated using the areas of the monomer ~ ( 0 1 4 ) band.…”