Determination of the semiexperimental equilibrium structure of 2-acetylthiophene in the presence of methyl internal rotation and substituent effects compared to thiophene - Archive ouverte HAL Access content directly
Journal Articles Physical Chemistry Chemical Physics Year : 2022

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

Christina Dindić
  • Function : Author
Jil Ludovicy
  • Function : Author
Vladimir Terzi
  • Function : Author
Arne Lüchow
  • Function : Author
Natalja Vogt
  • Function : Author
Jean Demaison
  • Function : Author

Abstract

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 syn and an anti orientation of the S1–C2 and C6=O bonds (with respect to the C2–C6 bond) were identified, and the syn-conformer was more stable. The spectra of the 34S- and 13C-isotopologues of syn-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−1 for the syn-conformer and the anti-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.
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hal-03592004 , version 1 (01-03-2022)

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Christina Dindić, Jil Ludovicy, Vladimir Terzi, Arne Lüchow, Natalja Vogt, et al.. Determination of the semiexperimental equilibrium structure of 2-acetylthiophene in the presence of methyl internal rotation and substituent effects compared to thiophene. Physical Chemistry Chemical Physics, 2022, 24, pp.3804-3815. ⟨10.1039/D1CP04478H⟩. ⟨hal-03592004⟩
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