Details
| Original language | English |
|---|---|
| Article number | 2639 |
| Journal | MOLECULES |
| Volume | 27 |
| Issue number | 9 |
| Early online date | 20 Apr 2022 |
| Publication status | Published - 1 May 2022 |
Abstract
The gas-phase structures of the fruit ester methyl hexanoate, CH3-O-(C=O)-C5 H11, have been determined using a combination of molecular jet Fourier-transform microwave spectroscopy and quantum chemistry. The microwave spectrum was measured in the frequency range of 3 to 23 GHz. Two conformers were assigned, one with Cs symmetry and the other with C1 symmetry where the γ-carbon atom of the hexyl chain is in a gauche orientation in relation to the carbonyl bond. Splittings of all rotational lines into doublets were observed due to internal rotation of the methoxy methyl group CH3-O, from which torsional barriers of 417 cm−1 and 415 cm−1, respectively, could be deduced. Rotational constants obtained from geometry optimizations at various levels of theory were compared to the experimental values, confirming the soft degree of freedom of the (C=O)-C bond observed for the C1 conformer of shorter methyl alkynoates like methyl butyrate and methyl valerate. Comparison of the barriers to methyl internal rotation of methyl hexanoate to those of other CH3-O-(C=O)-R molecules leads to the conclusion that though the barrier height is relatively constant at about 420 cm−1, it decreases in molecules with longer R.
Keywords
- internal rotation, large amplitude motion, microwave spectroscopy, rotational spectroscopy
ASJC Scopus subject areas
- Chemistry(all)
- Analytical Chemistry
- Chemistry(all)
- Chemistry (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Molecular Medicine
- Pharmacology, Toxicology and Pharmaceutics(all)
- Pharmaceutical Science
- Pharmacology, Toxicology and Pharmaceutics(all)
- Drug Discovery
- Chemistry(all)
- Physical and Theoretical Chemistry
- Chemistry(all)
- Organic Chemistry
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In: MOLECULES, Vol. 27, No. 9, 2639, 01.05.2022.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Methyl Internal Rotation in Fruit Esters
T2 - Chain-Length Effect Observed in the Microwave Spectrum of Methyl Hexanoate
AU - Dang, Nhu Ngoc
AU - Pham, Hoang Nam
AU - Kleiner, Isabelle
AU - Schwell, Martin
AU - Grabow, Jens Uwe
AU - Nguyen, Ha Vinh Lam
N1 - Funding Information: Funding: This research was funded by the Agence Nationale de la Recherche (ANR), grant number ANR-18-CE29-0011 and the Deutsche Forschungsgemeinschaft (DFG), grant number GR1344/4-1, 4-2, 4-3.
PY - 2022/5/1
Y1 - 2022/5/1
N2 - The gas-phase structures of the fruit ester methyl hexanoate, CH3-O-(C=O)-C5 H11, have been determined using a combination of molecular jet Fourier-transform microwave spectroscopy and quantum chemistry. The microwave spectrum was measured in the frequency range of 3 to 23 GHz. Two conformers were assigned, one with Cs symmetry and the other with C1 symmetry where the γ-carbon atom of the hexyl chain is in a gauche orientation in relation to the carbonyl bond. Splittings of all rotational lines into doublets were observed due to internal rotation of the methoxy methyl group CH3-O, from which torsional barriers of 417 cm−1 and 415 cm−1, respectively, could be deduced. Rotational constants obtained from geometry optimizations at various levels of theory were compared to the experimental values, confirming the soft degree of freedom of the (C=O)-C bond observed for the C1 conformer of shorter methyl alkynoates like methyl butyrate and methyl valerate. Comparison of the barriers to methyl internal rotation of methyl hexanoate to those of other CH3-O-(C=O)-R molecules leads to the conclusion that though the barrier height is relatively constant at about 420 cm−1, it decreases in molecules with longer R.
AB - The gas-phase structures of the fruit ester methyl hexanoate, CH3-O-(C=O)-C5 H11, have been determined using a combination of molecular jet Fourier-transform microwave spectroscopy and quantum chemistry. The microwave spectrum was measured in the frequency range of 3 to 23 GHz. Two conformers were assigned, one with Cs symmetry and the other with C1 symmetry where the γ-carbon atom of the hexyl chain is in a gauche orientation in relation to the carbonyl bond. Splittings of all rotational lines into doublets were observed due to internal rotation of the methoxy methyl group CH3-O, from which torsional barriers of 417 cm−1 and 415 cm−1, respectively, could be deduced. Rotational constants obtained from geometry optimizations at various levels of theory were compared to the experimental values, confirming the soft degree of freedom of the (C=O)-C bond observed for the C1 conformer of shorter methyl alkynoates like methyl butyrate and methyl valerate. Comparison of the barriers to methyl internal rotation of methyl hexanoate to those of other CH3-O-(C=O)-R molecules leads to the conclusion that though the barrier height is relatively constant at about 420 cm−1, it decreases in molecules with longer R.
KW - internal rotation
KW - large amplitude motion
KW - microwave spectroscopy
KW - rotational spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85129308889&partnerID=8YFLogxK
U2 - 10.3390/molecules27092639
DO - 10.3390/molecules27092639
M3 - Article
C2 - 35565991
AN - SCOPUS:85129308889
VL - 27
JO - MOLECULES
JF - MOLECULES
SN - 1420-3049
IS - 9
M1 - 2639
ER -