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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.


Scan of the potential energy surface calculated along the dihedral angle τ1 (H11– C7– C2– C1) according to the labeling in Figure 2 at the B3LYP/6-311++G(d,p) level of theory for (-)-menthone. The position of each minimum conformation (A, B, C) is indicated in the plot and illustrated with the corresponding structure.
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Figure 7: Scan of the potential energy surface calculated along the dihedral angle τ1 (H11– C7– C2– C1) according to the labeling in Figure 2 at the B3LYP/6-311++G(d,p) level of theory for (-)-menthone. The position of each minimum conformation (A, B, C) is indicated in the plot and illustrated with the corresponding structure.

Mentions: According to NMR measurements and quantum chemical calculations by Smith et al., the cyclohexane ring in menthone is in the chair configuration and both substituents, the isopropyl and the methyl groups, are in equatorial positions (Smith and Amezcua, 1998). Hence the degrees of freedom of menthone are limited to the rotations of the isopropyl and methyl groups. We calculated the relaxed potential energy surface for the rotation of the isopropyl group [dihedral angle τ1 (H11-C7-C2-C1)] at the B3LYP/6-311++G(d,p) level of theory. The result is displayed in Figure 7 and exhibits three different minima at orientations similar to those of (-)-menthol. These three structures were optimized at the B3LYP/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and MP2/6-311++G(d,p) levels of theory. The results are summarized in Table 4. The zero-point corrected energies of the three menthone rotamers are within 3 kJ/mol (B3LYP/aug-cc-pVTZ calculation) of each other.


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

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

Scan of the potential energy surface calculated along the dihedral angle τ1 (H11– C7– C2– C1) according to the labeling in Figure 2 at the B3LYP/6-311++G(d,p) level of theory for (-)-menthone. The position of each minimum conformation (A, B, C) is indicated in the plot and illustrated with the corresponding structure.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Scan of the potential energy surface calculated along the dihedral angle τ1 (H11– C7– C2– C1) according to the labeling in Figure 2 at the B3LYP/6-311++G(d,p) level of theory for (-)-menthone. The position of each minimum conformation (A, B, C) is indicated in the plot and illustrated with the corresponding structure.
Mentions: According to NMR measurements and quantum chemical calculations by Smith et al., the cyclohexane ring in menthone is in the chair configuration and both substituents, the isopropyl and the methyl groups, are in equatorial positions (Smith and Amezcua, 1998). Hence the degrees of freedom of menthone are limited to the rotations of the isopropyl and methyl groups. We calculated the relaxed potential energy surface for the rotation of the isopropyl group [dihedral angle τ1 (H11-C7-C2-C1)] at the B3LYP/6-311++G(d,p) level of theory. The result is displayed in Figure 7 and exhibits three different minima at orientations similar to those of (-)-menthol. These three structures were optimized at the B3LYP/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and MP2/6-311++G(d,p) levels of theory. The results are summarized in Table 4. The zero-point corrected energies of the three menthone rotamers are within 3 kJ/mol (B3LYP/aug-cc-pVTZ calculation) of each other.

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.