n-Alkanols can occur in a multitude of energetically competitive conformational states. Using the OH stretching vibration as an infrared and Raman spectroscopic sensor in supersonic jet expansions, the torsional preferences around the Calpha-O and Cbeta-Calpha bonds are probed for n-propanol through n-hexanol. Raman detection is more powerful for isolated monomers, whereas IR spectroscopy is more sensitive for molecular complexes. The subtle IR vibrational shift induced by the nanocoating of n-alcohols with Ar atoms is shown to alternate with chain length. A large number of alcohol dimer absorptions is observed and subjected to collisional relaxation and nanocoating conditions. Essential features of the dimer spectra are modeled successfully by a simple force field approach. Exploratory quantum chemical calculations up to the MP2/aug-cc-pvqz level encourage a rigorous theoretical study of the subtle conformational aspects in monomers and possibly also in dimers of linear alcohols.

The aggregation behavior of racemic and enantiopure 1-indanol has been studied by FTIR spectroscopy, resonant ion dip IR spectroscopy, and spontaneous Raman scattering in supersonic jets. This triple experimental approach, augmented by homology to related molecular fragments and dispersion-corrected DFT predictions, allows disentangling the complex spectroscopic signature in the OH stretch range. Evidence for chirality-sensitive aggregation via isolated OH···π bonds in competition with cooperative ···OH···OH···π patterns is collected. An accurate description of London dispersion forces provides the key to its explanation.

Supersonic jet FTIR spectroscopy supplemented by 18O substitution shows unambiguously that water prefers to act as an O−H⋅⋅⋅N hydrogen bond donor towards imidazole, instead of acting as a N−H⋅⋅⋅O acceptor. Previous matrix isolation, helium droplet, and aromatic substitution experiments had remained ambiguous, as are standard quantum chemical calculations. The finding is supported by a study of the analogous methanol complexes and by higher level quantum chemical calculations.

Supersonic jet Raman spectroscopy reveals an increasing bathochromic shift of the OH stretching vibration in the most stable conformation of propanol with increasing extent of argon nanocoating. It falls short of the bulk matrix limit of 17 cm−1 even at large nozzle distances. Quantum chemical harmonic frequency calculations up to the CCSD(T) level show that this shift cannot be accounted for by individual Ar atoms or even a first solvation layer but instead requires several layers of Ar atoms around the molecule to be explained. It is shown that the stability of Ar−propanol clusters correlates with the number of close O and C contacts to the Ar and that bathochromic shifts are largely caused by backbone solvation. Hydrogen-bonding OH solvation tends to slightly increase the OH stretching frequency but is very sensitive to the computational level.

Carbohydrates are used in nature as molecular recognition tools. Understanding their conformational behavior upon aggregation helps in rationalizing the way in which cells and bacteria use sugars to communicate. Here, the simplest α-hydroxy carbonyl compound, glycolaldehyde, was used as a model system. It was shown to form compact polar C2-symmetric dimers with intermolecular O–H⋅⋅⋅O=C bonds, while sacrificing the corresponding intramolecular hydrogen bonds. Supersonic jet infrared (IR) and Raman spectra combined with high-level quantum chemical calculations provide a consistent picture for the preference over more typical hydrogen bond insertion and addition patterns. Experimental evidence for at least one metastable dimer is presented. A rotational spectroscopy investigation of these dimers is encouraged, also in view of astrophysical searches. The binding motif competition of aldehydic sugars might play a role in chirality recognition phenomena of more complex derivatives in the gas phase.