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Exploring the conformational landscape of menthol, menthone, and isomenthone: a microwave study.

Schmitz D, Shubert VA, Betz T, Schnell M - Front Chem (2015)

Bottom Line: For menthol only one conformation was identified under the cold conditions of the molecular jet, whereas three conformations were observed for menthone and one for isomenthone.The conformational space of the different molecules was extensively studied using quantum chemical calculations, and the results were compared with molecular parameters obtained by the measurements.Finally, a computer program is presented, which automatically identifies different species in a dense broadband microwave spectrum using calculated ab initio rotational constants as initial input parameters.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for the Structure and Dynamics of Matter Hamburg, Germany ; The Center for Free-Electron Laser Science Hamburg, Germany.

ABSTRACT
The rotational spectra of the monoterpenoids menthol, menthone, and isomenthone are reported in the frequency range of 2-8.5 GHz, obtained with broadband Fourier-transform microwave spectroscopy. For menthol only one conformation was identified under the cold conditions of the molecular jet, whereas three conformations were observed for menthone and one for isomenthone. The conformational space of the different molecules was extensively studied using quantum chemical calculations, and the results were compared with molecular parameters obtained by the measurements. Finally, a computer program is presented, which automatically identifies different species in a dense broadband microwave spectrum using calculated ab initio rotational constants as initial input parameters.

No MeSH data available.


Related in: MedlinePlus

Plot of the potential energy landscape of (-)-menthol as a function of the isopropyl and the hydroxyl dihedral angles. The data was extracted from a two-dimensional, relaxed potential energy scan using the B3LYP/3-21G functional. The dashed lines mark cuts through the 3D surface, which were evaluated using a higher level of theory (B3LYP/6-311++G(d,p)). The results of these three scans are depicted in Figure 5.
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Figure 4: Plot of the potential energy landscape of (-)-menthol as a function of the isopropyl and the hydroxyl dihedral angles. The data was extracted from a two-dimensional, relaxed potential energy scan using the B3LYP/3-21G functional. The dashed lines mark cuts through the 3D surface, which were evaluated using a higher level of theory (B3LYP/6-311++G(d,p)). The results of these three scans are depicted in Figure 5.

Mentions: It was shown by NMR spectroscopy, gas phase electron diffraction, and several quantum chemical computation studies that the chair conformation of cyclohexane is preferred in menthol (Egawa et al., 2003; Härtner and Reinscheid, 2008). In order to get an overview of the potential energy surface, we performed a relaxed two dimensional scan at the B3LYP/3-21G level of theory by rotating the isopropyl and hydroxyl groups with all three substituents in equatorial positions. The rotation of the hydroxyl group with respect to the ring occurs around the dihedral angle τ2 (H12-O-C1-C2), while the isopropyl orientation is described with the dihedral angle τ1 (H11-C7-C2-C1) (compare Figure 1). The resulting PES is shown in Figure 4 and reveals the existence of various stable rotamers. In this figure we mark the nine lowest energy rotamers using the labeling scheme introduced by Avilés Moreno et al. (2013).


Exploring the conformational landscape of menthol, menthone, and isomenthone: a microwave study.

Schmitz D, Shubert VA, Betz T, Schnell M - Front Chem (2015)

Plot of the potential energy landscape of (-)-menthol as a function of the isopropyl and the hydroxyl dihedral angles. The data was extracted from a two-dimensional, relaxed potential energy scan using the B3LYP/3-21G functional. The dashed lines mark cuts through the 3D surface, which were evaluated using a higher level of theory (B3LYP/6-311++G(d,p)). The results of these three scans are depicted in Figure 5.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355985&req=5

Figure 4: Plot of the potential energy landscape of (-)-menthol as a function of the isopropyl and the hydroxyl dihedral angles. The data was extracted from a two-dimensional, relaxed potential energy scan using the B3LYP/3-21G functional. The dashed lines mark cuts through the 3D surface, which were evaluated using a higher level of theory (B3LYP/6-311++G(d,p)). The results of these three scans are depicted in Figure 5.
Mentions: It was shown by NMR spectroscopy, gas phase electron diffraction, and several quantum chemical computation studies that the chair conformation of cyclohexane is preferred in menthol (Egawa et al., 2003; Härtner and Reinscheid, 2008). In order to get an overview of the potential energy surface, we performed a relaxed two dimensional scan at the B3LYP/3-21G level of theory by rotating the isopropyl and hydroxyl groups with all three substituents in equatorial positions. The rotation of the hydroxyl group with respect to the ring occurs around the dihedral angle τ2 (H12-O-C1-C2), while the isopropyl orientation is described with the dihedral angle τ1 (H11-C7-C2-C1) (compare Figure 1). The resulting PES is shown in Figure 4 and reveals the existence of various stable rotamers. In this figure we mark the nine lowest energy rotamers using the labeling scheme introduced by Avilés Moreno et al. (2013).

Bottom Line: For menthol only one conformation was identified under the cold conditions of the molecular jet, whereas three conformations were observed for menthone and one for isomenthone.The conformational space of the different molecules was extensively studied using quantum chemical calculations, and the results were compared with molecular parameters obtained by the measurements.Finally, a computer program is presented, which automatically identifies different species in a dense broadband microwave spectrum using calculated ab initio rotational constants as initial input parameters.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for the Structure and Dynamics of Matter Hamburg, Germany ; The Center for Free-Electron Laser Science Hamburg, Germany.

ABSTRACT
The rotational spectra of the monoterpenoids menthol, menthone, and isomenthone are reported in the frequency range of 2-8.5 GHz, obtained with broadband Fourier-transform microwave spectroscopy. For menthol only one conformation was identified under the cold conditions of the molecular jet, whereas three conformations were observed for menthone and one for isomenthone. The conformational space of the different molecules was extensively studied using quantum chemical calculations, and the results were compared with molecular parameters obtained by the measurements. Finally, a computer program is presented, which automatically identifies different species in a dense broadband microwave spectrum using calculated ab initio rotational constants as initial input parameters.

No MeSH data available.


Related in: MedlinePlus