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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.


Results for the subcube shaded red in Figure 9. (A) Sample distribution after the fit employing SPFIT (step 2). The samples are color-coded using the value of the standard deviation provided by SPFIT. A subtle convergence toward the measured value (green triangle) is visible. (B) Sample distribution after evaluation of the fitting results (step 3). The samples are now color-coded using the number of assigned lines of the SPCAT prediction. The concentration of many samples at the measured rotational constants and the color-code of the samples indicates a correctly assigned spectrum (up to 18 assigned transitions). The comparison of (A,B) illustrates the necessity of the evaluation step 3. Good and bad fitting results are scattered throughout the volume in (A), but (B) reveals that the samples far away from real values predict spectra which have little overlap with the measured one.
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Figure 10: Results for the subcube shaded red in Figure 9. (A) Sample distribution after the fit employing SPFIT (step 2). The samples are color-coded using the value of the standard deviation provided by SPFIT. A subtle convergence toward the measured value (green triangle) is visible. (B) Sample distribution after evaluation of the fitting results (step 3). The samples are now color-coded using the number of assigned lines of the SPCAT prediction. The concentration of many samples at the measured rotational constants and the color-code of the samples indicates a correctly assigned spectrum (up to 18 assigned transitions). The comparison of (A,B) illustrates the necessity of the evaluation step 3. Good and bad fitting results are scattered throughout the volume in (A), but (B) reveals that the samples far away from real values predict spectra which have little overlap with the measured one.

Mentions: Scheme of the sampling volume of the rotational constants for the computer aided assignment routine. The cubic sampling volume is divided into eight subcubes and the routine is carried out consecutively in each of the subcubes. Afterwards the results of the individual subcubes are compared. The blue diamond in the center indicates the position of the calculated rotational constants and the green triangle indicates the position of the experimentally obtained value for isomenthone eq-ax A. The red shaded area is used to display the results in Figure 10.


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

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

Results for the subcube shaded red in Figure 9. (A) Sample distribution after the fit employing SPFIT (step 2). The samples are color-coded using the value of the standard deviation provided by SPFIT. A subtle convergence toward the measured value (green triangle) is visible. (B) Sample distribution after evaluation of the fitting results (step 3). The samples are now color-coded using the number of assigned lines of the SPCAT prediction. The concentration of many samples at the measured rotational constants and the color-code of the samples indicates a correctly assigned spectrum (up to 18 assigned transitions). The comparison of (A,B) illustrates the necessity of the evaluation step 3. Good and bad fitting results are scattered throughout the volume in (A), but (B) reveals that the samples far away from real values predict spectra which have little overlap with the measured one.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 10: Results for the subcube shaded red in Figure 9. (A) Sample distribution after the fit employing SPFIT (step 2). The samples are color-coded using the value of the standard deviation provided by SPFIT. A subtle convergence toward the measured value (green triangle) is visible. (B) Sample distribution after evaluation of the fitting results (step 3). The samples are now color-coded using the number of assigned lines of the SPCAT prediction. The concentration of many samples at the measured rotational constants and the color-code of the samples indicates a correctly assigned spectrum (up to 18 assigned transitions). The comparison of (A,B) illustrates the necessity of the evaluation step 3. Good and bad fitting results are scattered throughout the volume in (A), but (B) reveals that the samples far away from real values predict spectra which have little overlap with the measured one.
Mentions: Scheme of the sampling volume of the rotational constants for the computer aided assignment routine. The cubic sampling volume is divided into eight subcubes and the routine is carried out consecutively in each of the subcubes. Afterwards the results of the individual subcubes are compared. The blue diamond in the center indicates the position of the calculated rotational constants and the green triangle indicates the position of the experimentally obtained value for isomenthone eq-ax A. The red shaded area is used to display the results in Figure 10.

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.