Determination of the semiexperimental equilibrium structure of 2-acetylthiophene in the presence of methyl internal rotation and substituent effects compared to thiophene

Determination of the semiexperimental equilibrium structure of 2-acetylthiophene in the presence of methyl internal rotation and substituent effects compared to thiophene

The microwave spectra of thiophene and 2-acetylthiophene were recorded in the frequency range from 2 to 40 GHz using two molecular jet Fourier transform microwave spectrometers. For 2-acetylthiophene, two conformers with a and an orientation of the S1-C2 and C6O bonds (with respect to the C2-C6 bon...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP Vol. 24; no. 6; p. 3804
Main Authors: Dindić, Christina, Ludovicy, Jil, Terzi, Vladimir, Lüchow, Arne, Vogt, Natalja, Demaison, Jean, Nguyen, Ha Vinh Lam
Format: Journal Article
Language:English
Published: England 09-02-2022
Subjects:
Fourier Analysis
Microwaves
Molecular Conformation
Thiophenes
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Summary:The microwave spectra of thiophene and 2-acetylthiophene were recorded in the frequency range from 2 to 40 GHz using two molecular jet Fourier transform microwave spectrometers. For 2-acetylthiophene, two conformers with a and an orientation of the S1-C2 and C6O bonds (with respect to the C2-C6 bond) were identified, and the -conformer was more stable. The spectra of the S- and C-isotopologues of -2-acetylthiophene were also assigned, and the semiexperimental equilibrium structure could be determined. Compared to thiophene, at the substitution position, the S1-C2 and C2C3 bond lengths both increase by about 0.007 Å, and the bond angle S1-C2C3 decreases by 0.06°, noticeably larger than the experimental uncertainties. A-E torsional splittings were observed due to internal rotation of the methyl group hindered by a barrier height of 330.187(35) and 295.957(17) cm for the -conformer and the -conformer, respectively. Geometry and internal rotation parameters are compared with those of related thiophene derivatives, as well as those of furan and 2-acetylthiophene to gain a better understanding of structure determination in the presence of methyl internal rotation.
ISSN:1463-9084
DOI:10.1039/d1cp04478h