Spectroscopic and Theoretical Study of the Intramolecular π‑Type Hydrogen Bonding and Conformations of 2‑Cyclohexen-1-ol

The infrared and Raman spectra of 2-cyclohexen-1-ol have been recorded and analyzed. The experimental work has been complemented by ab initio and density functional theory computations. The calculations show that in the vapor phase the conformations with the π-type hydrogen bonding are the lowest in energy, and these findings are supported by the experimental spectra, which agree well with the theoretical predictions. The six conformers predicted result from differences between the direction on the ring-twisting angle and the −OH internal rotation angle. The lowest-energy conformer has the hydrogen of the OH group pointing to the middle of the CC double bond. The other conformers are calculated to be 72 cm^–1 (0.21 kcal/mol) to 401 cm^–1 (1.15 kcal/mol) higher in energy. In the liquid phase, only two conformers can be identified in the spectra, and these correspond to different directions of the ring-twisting.