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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 (-)-isomenthone eq-eq, (-)-isomenthone ax-eq and (-)-isomenthone eq-ax. The labels A–C are pointing to the corresponding minima. Only the conformation isomenthone eq-ax A was observed in the microwave spectrum.
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Figure 8: 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 (-)-isomenthone eq-eq, (-)-isomenthone ax-eq and (-)-isomenthone eq-ax. The labels A–C are pointing to the corresponding minima. Only the conformation isomenthone eq-ax A was observed in the microwave spectrum.

Mentions: Again we performed a relaxed potential energy scan by rotating the isopropyl group around the dihedral angle τ1 for the three different starting structures (-)-isomenthone eq-ax, (-)-isomenthone ax-eq and (-)-isomenthone eq-eq. Figure 8 shows the results for these relaxed potential energy scans. The global minimum was found for (-)-isomenthone eq-ax at about τ1 = −60°. Therefore, the set of conformers with τ1 being close to −60° is labeled as A. The set of minimum structures at τ1 ≈ −45° is labeled as B, and the set at τ1 ≈ −180° is labeled as C. For all nine minimum structures, optimizations and frequency calculations were carried out using the B3LYP/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and MP2/6-311++G(d,p) levels of theory. The results of these calculations for the three lowest energy structures (isomenthone eq-ax A, isomenthone ax-eq A, and isomenthone ax-eq B) are listed in Table 5. The dipole moment components and the dihedral angle of the isopropyl group are given for the (-)-enantiomers.


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 (-)-isomenthone eq-eq, (-)-isomenthone ax-eq and (-)-isomenthone eq-ax. The labels A–C are pointing to the corresponding minima. Only the conformation isomenthone eq-ax A was observed in the microwave spectrum.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 8: 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 (-)-isomenthone eq-eq, (-)-isomenthone ax-eq and (-)-isomenthone eq-ax. The labels A–C are pointing to the corresponding minima. Only the conformation isomenthone eq-ax A was observed in the microwave spectrum.
Mentions: Again we performed a relaxed potential energy scan by rotating the isopropyl group around the dihedral angle τ1 for the three different starting structures (-)-isomenthone eq-ax, (-)-isomenthone ax-eq and (-)-isomenthone eq-eq. Figure 8 shows the results for these relaxed potential energy scans. The global minimum was found for (-)-isomenthone eq-ax at about τ1 = −60°. Therefore, the set of conformers with τ1 being close to −60° is labeled as A. The set of minimum structures at τ1 ≈ −45° is labeled as B, and the set at τ1 ≈ −180° is labeled as C. For all nine minimum structures, optimizations and frequency calculations were carried out using the B3LYP/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and MP2/6-311++G(d,p) levels of theory. The results of these calculations for the three lowest energy structures (isomenthone eq-ax A, isomenthone ax-eq A, and isomenthone ax-eq B) are listed in Table 5. The dipole moment components and the dihedral angle of the isopropyl group are given for the (-)-enantiomers.

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.