Two methyl internal rotations of 2-acetyl-4-methylthiophene explored by microwave spectroscopy and quantum chemistry

Dindić, Christina; Barth, Mike; Nguyen, Ha Vinh Lam

doi:10.1016/j.saa.2022.121505

Cited by 8 publications

(29 citation statements)

References 76 publications

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“…The only case where the addition of the acetyl group leads to an increase in the barrier to methyl internal rotation is anti-2-acetyl-3-methylthiophene (1) (321.8 cm −1 ) [193], compared to 3-methylthiophene (258.8 cm −1 , molecule (2) in Figure 3) [97], due to steric hindrance between the methyl group attached to the ring and the acetyl group. The orientation of the acetyl group has only negligible influences on the barrier of the ring methyl rotor as can be seen in the cases of syn-2-acetyl-4-methylthiophene (2a) (210.7 cm −1 ) and anti-2-acetyl-4-methylthiophene (2b) (213.0 cm −1 ) [194].…”

Section: Methyl Substitution On a Substituentmentioning

confidence: 93%

“…The furan and thiophene derivatives illustrated in Figure 11 all possess a methyl group attached to the ring and an acetyl methyl group. (1) anti-2-acetyl-3-methylthiophene [193], (2) 2-acetyl-4-methylthiophene [194], (3) syn-2-acetyl-5methylthiophene [195], (4) 2-acetyl-5-methylfuran [86].…”

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

“…The effect is reported to be stronger for linear aliphatic ketones with a C s structure and thus a "straighter" chain than those with a C 1 structure and a "bent" chain. 5) anti-2acetyl-3-methylthiophene [193], (6) anti-2-acetyl-4-methylthiophene [194], (7) syn-2-acetyl-5methylthiophene [195], (8) syn-2-acetyl-5-methylfuran [86], (9) anti-2-acetyl-5-methylfuran [86].…”

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

“…We found the same situation while comparing the molecules in Figure 12. In anti-2acetyl-4-methylthiophene (6) [194] (−14.8 cm −1 compared to anti-2-acetylthiophene (1) [132]), syn-2-acetyl-5-methylthiophene (7) [195] (−28.4 cm −1 compared to syn-2-acetylthiophene (2) [132]), syn-2-acetyl-5-methylfuran (8) [86] (−27.1 cm −1 compared to syn-2-acetylfuran (3) [133]), the acetyl methyl and ring methyl group lie on a straight chain (marked by a dotted line in Figure 12), and the torsional barrier of the acetyl methyl rotor decreases more than it does for anti-2-acetyl-5-methylfuran (9) (−12.0 cm −1 compared to anti-2-acetylfuran (4)). In anti-2-acetyl-3-methylthiophene (5) [193], the additional methyl group at the 3-position of the ring makes the molecule more globular than anti-2-acetylthiophene (1).…”

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

“…Barriers to methyl internal rotation in furan and thiophene derivatives with a methyl rotor on the ring and an acetyl group which contains another methyl rotor (in cm −1 ). (1) anti-2-acetyl-3-methylthiophene[193], (2) 2-acetyl-4-methylthiophene[194], (3) syn-2-acetyl-5methylthiophene[195], (4) 2-acetyl-5-methylfuran[86].…”

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The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

2022

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Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five- and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives. Such systems are ideally suited to create families of molecules in which the positions and the number of LAMs can be varied, while the heteroatoms often provide a sufficient dipole moment to the systems to warrant the observation of their rotational spectra. This review will summarize three types of LAMs: internal rotation, inversion tunneling, and ring puckering, which are frequently observed in aromatic five-membered rings such as furan, thiophene, pyrrole, thiazole, and oxazole derivatives, in aromatic six-membered rings such as benzene, pyridine, and pyrimidine derivatives, and larger combined rings such as naphthalene, indole, and indan derivatives. For each molecular class, we will present the representatives and summarize the recent insights on the molecular structure and internal dynamics and how they help to advance the field of quantum mechanics.

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Section: Methyl Substitution On a Substituentmentioning

confidence: 93%

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

Section: Methyl Substitution On a Substituentmentioning

confidence: 99%

mentioning

confidence: 99%

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The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

2022

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Low Barrier Methyl Internal Rotations and ¹⁴N Quadrupole Coupling in the Microwave Spectrum of 2,4-Dimethylthiazole

et al. 2023

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The microwave spectrum of 2,4-dimethylthiazole was recorded using a pulsed molecular jet Fourier-transform microwave spectrometer operating in the frequency range from 2.0 to 26.5 GHz. Torsional splittings into quintets were observed for all rotational transitions due to internal rotations of two inequivalent methyl groups. Hyperfine structures arising from the nuclear quadrupole coupling of the 14 N nucleus were fully resolved. The microwave spectra were analyzed using the modified version of the XIAM code and the BELGI-C s -2Tops-hyperfine code. The barriers to methyl internal rotation of the 4-and 2-methyl groups were determined to be 396.707(25) cm −1 and 19.070(58) cm −1 , respectively. The very low barrier hindering the 2-methyl torsion was a challenge for the spectral analysis and modeling, and separately fitting the five torsional species together with combination difference loops was the key for a successful assignment. The methyl torsional barriers were compared with those of other thiazole derivatives, showing the influence of the methyl group position on the barrier height. The experimental results were supported by quantum chemical calculations.

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Benchmarking acetylthiophene derivatives: methyl internal rotations in the microwave spectrum of 2-acetyl-5-methylthiophene

Dindić

Nguyen

2023

Phys. Chem. Chem. Phys.

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Two methyl internal rotations of 2-acetyl-4-methylthiophene explored by microwave spectroscopy and quantum chemistry

Cited by 8 publications

References 76 publications

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

Low Barrier Methyl Internal Rotations and ¹⁴N Quadrupole Coupling in the Microwave Spectrum of 2,4-Dimethylthiazole

Benchmarking acetylthiophene derivatives: methyl internal rotations in the microwave spectrum of 2-acetyl-5-methylthiophene

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Two methyl internal rotations of 2-acetyl-4-methylthiophene explored by microwave spectroscopy and quantum chemistry

Cited by 8 publications

References 76 publications

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy

Low Barrier Methyl Internal Rotations and 14N Quadrupole Coupling in the Microwave Spectrum of 2,4-Dimethylthiazole

Benchmarking acetylthiophene derivatives: methyl internal rotations in the microwave spectrum of 2-acetyl-5-methylthiophene

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Low Barrier Methyl Internal Rotations and ¹⁴N Quadrupole Coupling in the Microwave Spectrum of 2,4-Dimethylthiazole