Conformational sampling and large amplitude motion of methyl valerate
Ha Vinh Lam Nguyen1, Maike Andresen2, Wolfgang Stahl3
1Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583, Université Paris-Est Créteil, Université Paris Diderot, Institut Pierre Simon Laplace, 61 avenue du Général de Gaulle, F-94010 Créteil cedex, France. lam.nguyen@lisa.u-pec.fr and Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris cedex 05, France.
Physical Chemistry Chemical Physics : PCCP
|January 22, 2021
Summary
The microwave spectrum of methyl valerate was analyzed, revealing two conformers. The internal rotation barrier of the methoxy methyl group was determined, consistent with shorter chain esters.
Area of Science:
- Molecular spectroscopy
- Quantum chemistry
- Physical organic chemistry
Background:
- Methyl valerate, a fruit ester, is important in flavor and fragrance industries.
- Understanding its molecular structure and dynamics is crucial for predicting its properties.
Purpose of the Study:
- To experimentally determine the molecular structure and internal rotation dynamics of methyl valerate.
- To compare experimental findings with quantum chemical calculations.
Main Methods:
- Microwave spectroscopy using molecular jet Fourier transform spectrometers (2-40 GHz).
- Quantum chemical calculations (MP2/6-311++G(d,p) and MP2/cc-pVDZ) to predict structures and rotational constants.
- Analysis of torsional splittings in rotational transitions.
Main Results:
- Two anti ester conformers of methyl valerate were identified in the microwave spectrum.
- The barrier to internal rotation of the methoxy methyl group was determined to be approximately 418 cm-1 for both conformers.
- Rotational and centrifugal distortion constants were accurately determined.
- MP2/cc-pVDZ calculations successfully predicted rotational constants for conformer assignment, unlike MP2/6-311++G(d,p).
Conclusions:
- The determined internal rotation barrier is similar to that of shorter chain methyl alkanoates.
- Accurate structural parameters were obtained through microwave spectroscopy.
- The choice of quantum chemical method is critical for accurate prediction of rotational constants and conformer assignment.
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