Two equivalent methyl internal rotations in 2,5-dimethylthiophene investigated by microwave spectroscopy

Nguyen, Ha Vinh Lam

Permalink

https://hdl.handle.net/2142/91197 Copy

Description

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

Issue Date

2016-06-22

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

En

Permalink

http://hdl.handle.net/2142/91197

Copyright and License Information

Copyright 2016 by the authors

Owning Collections