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Phenyl- vs cyclohexyl-substitution in methanol: implications for the OH conformation and for dispersion-affected aggregation from vibrational spectra in supersonic jets.

Authors
  • Altnöder, Jonas
  • Oswald, Sönke
  • Suhm, Martin A
Type
Published Article
Journal
The Journal of Physical Chemistry A
Publisher
American Chemical Society
Publication Date
May 08, 2014
Volume
118
Issue
18
Pages
3266–3279
Identifiers
DOI: 10.1021/jp501763b
PMID: 24758292
Source
Medline
License
Unknown

Abstract

The monomers and hydrogen-bonded dimers of benzyl alcohol, cyclohexylmethanol, and 2-methyl-1-propanol are investigated by jet-FTIR spectroscopy, complemented by Raman spectra and quantum chemical calulations, including CCSD(T) corrections. A large variety of London dispersion effects from the interacting carbon cycles is revealed, sometimes adding to and sometimes competing with the alcoholic hydrogen bonds. Conformational (in-)flexibility provides the key for understanding these effects, and this requires accurate predictions of monomer conformational preferences, which are shown to be subtly at variance with experiment even for some triple-ζ MP2 calculations. In some observed dimers, cooperative OH···OH···π patterns are sacrificed to optimize σ-π dispersion interactions. In other competitive dimers, dispersion interactions are far from maximized, because that would imply a substantial weakening of the hydrogen bond. In the series from methanol dimer to 1-indanol dimer, which this contribution bridges, B3LYP-D3 appears to switch from an overestimation to a slight underestimation of cohesion, but overall it provides a very useful modeling tool for vibrational spectra of systems affected by both hydrogen bonds and London dispersion.

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