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The conformational landscape of myrtenol (2-Pinen-10-ol) and its robustness upon hydration was investigated theoretically and experimentally employing a synergic combination of quantum chemical calculations and Fourier transform microwave spectroscopy coupled to a supersonic jet expansion. Relaxed potential energy surfaces have been carried out and the lowest energy conformers of the monomer were found associated with different geometry of the hydroxymethyl group than those previously reported (G. Sedo et al, J. Mol. Spectrosc. 356 (2019) 32). Geometry optimizations and harmonic vibrational frequency calculations allowed to characterize the equilibrium structure of the possible conformers of myrtenol. Among the nine predicted structures, four have been observed, analyzed, and identified. The controversy on the geometry was solved with the deuteration of the hydroxyl group (OD), which led to the determination of substitution ( rs) geometry, in agreement with the present theoretical results. Interestingly, the four observed conformers exhibit the same orientation of OH as in the allyl alcohol molecule. Furthermore, hydrogen bonding linking myrtenol to water was studied. One monohydrate has been observed and identified. Non-covalent interactions (NCI) and NBO analysis were performed to depict the interactions responsible for the stabilization of the observed structure. We conclude that the structure of the hydroxymethyl group is robust and does not change upon hydration.

The gas-phase non-covalent interactions in the endo-fenchol···H2S and fenchone···H2S complexes have been unveiled using rotational spectroscopy in a supersonic jet expansion, and quantum chemical calculations. In endo-fenchol, the hydrogen bond...

The gas-phase rotational spectra of α-pinene oxide have been recorded using a chirped-pulse Fourier transform microwave spectrometer in the 6–18 GHz frequency range. The parent species and all heavy atom isotopologues (13C and 18O) have been observed in their natural abundance. The experimental rotational constants of all isotopic species observed have been determined and used to obtain the substitution (rs) and the effective (r0) structures of the most stable conformer of α-pinene oxide. Calculations using the density functional theories B3LYP, M06-2X, and MN15-L and the ab initio method MP2 level of theory were carried out to check their performance against experimental results. The structure of the heavy atom’s skeleton of α-pinene oxide has been compared to that of α-pinene and has shown that epoxidation does not overly affect the structure of the bicycle, validating its robustness. Furthermore, the structural features have been compared to those of other bicyclic molecules, such as nopinone and β-pinene.