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 Title: Two equivalent methyl internal rotations in 2,5-dimethylthiophene investigated by microwave spectroscopy Author(s): Nguyen, Ha Vinh Lam Contributor(s): Stahl, Wolfgang; Van, Vinh Subject(s): Spectroscopy of Large Amplitude Motions Abstract: The microwave spectrum of 2,5-dimethylthiophene, a sulfur-containing five-membered heterocyclic molecule with two conjugated double bonds, was recorded using two molecular beam Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Highly accurate molecular parameters were determined. The rotational constants obtained by geometry optimizations at different levels of theory are in good agreement with the experimental values. A C$_{2v}$ equilibrium structure was calculated, where one hydrogen atom of each methyl group is antiperiplanar to the sulfur atom, and the two methyl groups are thus equivalent. \newline \indent Transition states were optimized at different levels of theory using the Berny algorithm to calculate the barrier height of the two equivalent methyl rotors. The fitted experimental torsional barrier of 247.95594(30) \wn \ is in reasonable agreement with the calculated barriers. Similar barriers to internal rotation were found for the monomethyl derivatives 2-methylthiophene (194.1 \wn) and 3-methylthiophene (258.8 \wn). A labeling scheme for the group G$_{36}$ written as the semi-direct product (C$_{3}$$^{I} x C_{3}$$^{I}$) (x C$_{2v}$ was introduced. Issue Date: 2016-06-22 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91197 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2017-01-26
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