Acetyl Methyl Torsion in Pentan-2-one As Observed by Microwave Spectroscopy

Andresen, Maike; Kleiner, Isabelle; Schwell, Martin; Stahl, Wolfgang; Nguyen, Ha Vinh Lam

doi:10.1021/acs.jpca.8b06183

Cited by 24 publications

(89 citation statements)

References 37 publications

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“…A "pseudo-C s " conformation leads to a barrier height of approximately 180 cm À 1 and a C 1 conformation is connected to a value of about 240 cm À 1 . [45][46][47] In another study, Herbers et al pointed out that π-conjugations from the phenyl group significantly affect the acetyl methyl torsion of acetophenone derivatives and the barrier height raises to 600 cm À 1 . [44] Obviously, the methyl torsional barrier can be applied as a direct measure for steric and electronic contributions in the molecules.…”

Section: Discussionmentioning

confidence: 99%

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6‐Dimethylfluorobenzene

Khemissi

Nguyen

2020

ChemPhysChem

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Large amplitude motion of methyl groups in isolated molecules is a fundamental phenomenon in molecular physics. The methyl torsional barrier is sensitive to the steric and electronic environment in the surrounding of the methyl group, making the methyl group a detector of the molecular structure. To probe this eﬀect, the microwave spectrum of 2,6‐dimethylfluorobenzene, one of the six isomers of dimethylfluorobenzene, was measured using two pulsed molecular jet Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Due to internal rotations of two equivalent methyl groups with relatively low torsional barriers, all rotational transitions split into quartets with separations of up to several hundreds of MHz. The splittings were analyzed and modeled to deduce a torsional barrier of 236.7922 (21) cm−1. The results are compared to those obtained from quantum chemical calculations and with other fluorine substituted toluene derivatives of the current literature where the methyl group is adjacent to a fluorine atom.

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Section: Discussionmentioning

confidence: 99%

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6‐Dimethylfluorobenzene

Khemissi

Nguyen

2020

ChemPhysChem

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“…For example, the C 1 conformer of hexan-2-one [3] contains the C 1 conformer of pentan-2-one. [2] Based on the two conformers identified for heptan-2-one, [4] called the C s and the C 1 conformer, the geometry optimizations could hence be reduced to two calculations.…”

Section: Geometry Optimizationsmentioning

confidence: 99%

“…In many cases, its value is caused by structural aspects and functional groups of the molecule, making the internal rotor a spectroscopic "detector" of the structure. To explore this link between structural configurations and barriers in ketones, investigations on a series of saturated methyl n-alkyl ketones, including butan-2-one, [1] pentan-2-one, [2] hexan-2-one, [3] and heptan-2-one, [4] have been performed.…”

Section: Introductionmentioning

confidence: 99%

“…Conformers of the C 1 class always show a barrier to internal rotation of approximately 240 cm À 1 , while conformers of the C s class exhibit barrier heights around 180 cm À 1 . [2][3][4] In this work, the situation in ketones containing an acetyl methyl group will be further examined.…”

Section: Introductionmentioning

confidence: 99%

“…We were interested to find the limit of the plateau curve and decided to extend the series by studying octan-2-one, also called methyl hexyl ketone. As changes of the barrier heights induced by the alkyl chain length are rather small, the methyl alkyl ketone series is ideally suitable to study this effect because in the three previous investigations on pentan-2-one, [2] hexan-2-one, [3] and heptan-2-one [4] similar sets of parameters have been consistently applied. Since the values of the torsional barriers are quite sensitive to the set of parameters in use, this enables a reliable comparison.…”

Section: Introductionmentioning

confidence: 99%

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Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan‐2‐one

et al. 2020

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Methyl n-alkyl ketones form a class of molecules with interesting internal dynamics in the gas-phase. They contain two methyl groups undergoing internal rotations, the acetyl methyl group and the methyl group at the end of the alkyl chain. The torsional barrier of the acetyl methyl group is of special importance, since it allows for the discrimination of the conformational structures. As part of the series, the microwave spectrum of octan-2-one was recorded in the frequency range from 2 to 40 GHz, revealing two conformers, one with C 1 and one with C s symmetry. The barriers to internal rotation of the acetyl methyl group were determined to be 233.340(28) cm À 1 and 185.3490(81) cm À 1 , respectively, confirming the link between conformations and barrier heights already established for other methyl alkyl ketones. Extensive comparisons to molecules in the literature were carried out, and a small overview of general trends and rules concerning the acetyl methyl torsion is given. For the hexyl methyl group, the barrier height is 973.17(60) cm À 1 for the C 1 conformer and 979.62(69) cm À 1 for the C s conformer.

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Sensing the Molecular Structures of Hexan‐2‐one by Internal Rotation and Microwave Spectroscopy

et al. 2019

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Using two molecular jet Fourier transform spectrometers, the microwave spectrum of hexan‐2‐one, also called methyl n‐butyl ketone, was recorded in the frequency range from 2 to 40 GHz. Three conformers were assigned and fine splittings caused by the internal rotations of the two terminal methyl groups were analyzed. For the acetyl methyl group CH3COC3H6CH3, the torsional barrier is 186.9198(50) cm−1, 233.5913(97) cm−1, and 182.2481(25) cm−1 for the three observed conformers, respectively. The value of this parameter could be linked to the structure of the individual conformer, which enabled us to create a rule for predicting the barrier height of the acetyl methyl torsion in ketones. The very small splittings arising from the internal rotation of the butyl methyl group CH3COC3H6CH3 could be resolved as well, yielding the respective torsional barriers of 979.99(88) cm−1, 1016.30(77) cm−1, and 961.9(32) cm−1.

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Acetyl Methyl Torsion in Pentan-2-one As Observed by Microwave Spectroscopy

Cited by 24 publications

References 37 publications

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6‐Dimethylfluorobenzene

Two Equivalent Internal Rotations in the Microwave Spectrum of 2,6‐Dimethylfluorobenzene

Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan‐2‐one

Sensing the Molecular Structures of Hexan‐2‐one by Internal Rotation and Microwave Spectroscopy

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