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Conformational Analysis of Green Apple Flavour: The Gas‐Phase Structure of Ethyl Valerate Validated by Microwave Spectroscopy
Author(s) -
Mouhib H.,
Stahl W.
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100932
Subject(s) - conformational isomerism , rotational spectroscopy , chemistry , molecular beam , microwave , molecule , hyperfine structure , computational chemistry , analytical chemistry (journal) , atomic physics , organic chemistry , physics , quantum mechanics
We report on the microwave spectrum of ethyl valerate, C 4 H 9 ‐COO‐C 2 H 5 , observed by molecular beam Fourier transform microwave spectroscopy (MB‐FTMW). Highly accurate rotational and centrifugal distortion constants of the two most abundant conformers were determined. Their structure was investigated by comparison of the experimental rotational constants with those obtained by quantum chemical calculations. MP2/ 6‐311++G(d,p) calculations failed to give a proper description of the observed conformers in the supersonic jet. Therefore, also other basis sets were tried using Hartree–Fock, second‐order Møller–Plesset (MP2), and B3LYP methods to predict the observed gas‐phase structures of the molecule. The quantum chemical results guided the conformer assignment of the rotational constants, obtained from the microwave experiment. One of the two observed conformers has C s symmetry, while the most abundant conformer has C 1 symmetry. The main conformer possesses a strong spectrum with high intensities. Additionally, harmonic frequency calculations at different levels of theory where carried out and a low lying vibration of the entire n ‐butyl group against the rest of the molecule was identified. The symbiotic interplay of microwave gas‐phase investigations and quantum chemical calculations becomes evident in our results.