Tuning the Hydrogen Bond Donor/Acceptor Isomerism in Jet-Cooled Mixed Dimers of Aliphatic Alcohols

Abstract

Hydrogen bonded complexes between two different aliphatic alcohols exhibit donor/acceptor isomerism. In a supersonic jet expansion, the less stable isomer can isomerize to the more stable isomer if the energy difference is sufficiently large and the barrier sufficiently low. We show by FTIR jet spectroscopy that this is progressively the case for methanol/methanol-d1, methanol/ethanol, and methanol/tert-butyl alcohol, until no metastable donor/acceptor isomer persists in the expansion. Collisional relaxation experiments, 18O labeling and quantum chemical calculations are used to assign the spectra. Differences between energetical and spectroscopic acceptor strengths are discussed.

A combined Raman- and infrared jet study of mixed methanol–water and ethanol–water clusters

“…Which role each molecule assumes depends on the relative hydrogen bond donor-and acceptor strengths as well as on subtle secondary interactions. 28 Energetic donor/acceptor scales are particularly desirable, but difficult to extract from experiment. Furthermore, they are necessarily global in nature, integrating over all interaction sites.…”

“…The analysis of donor/acceptor preferences rests on the formalism presented in ref. 28 and spectroscopic excess quantities in the mixing process are compared to empirical correlations between thermodynamic and spectroscopic data. 29 Alcohol-water dimers provide valuable information on weak hydrogen bonds between C-H groups and oxygen atoms.…”

FTIR/PCA study of propanol in argon matrix: The initial stage of clustering and conformational transitions

“…The most significant results on this field have been obtained using the vibrational spectroscopy (FTIR absorption and Raman) together with trapping/isolation in various cryogenic matrices [4][5][6][7][8][9][10][11][12][13][14]. This is mainly because the spectral acquisition carried out on isolated clusters at very low temperatures causes the appearance of narrow peaks with minimal band overlapping.…”

Cold collisions catalyse conformational conversion

“…In a more recent study, Suhm and co-workers investigated the isomerism of jet-cooled, isotopically mixed methanol dimers (CH 3 OH-CH 3 OD) in a supersonic jet expansion. 10 They used Fourier transform infrared (FT-IR) absorption spectroscopy in the 3-4 mm (O-H and O-D stretch) region to study the degree of conformer conversion (or: donor/acceptor isomerism) in their 10-20 K jet expansion. A complication in the latter studies is that it is difficult to spectroscopically distinguish the mixed dimers from their homodimer counterparts.…”