The torsional barriers of two equivalent methyl internal rotations in 2,5-dimethylfuran investigated by microwave spectroscopy

Van, Vinh; Bruckhuisen, Jonas; Stahl, Wolfgang; Ilyushin, V. V.; Nguyen, Ha Vinh Lam

doi:10.1016/j.jms.2017.11.007

Cited by 35 publications

(36 citation statements)

References 28 publications

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“…Consequently, all rotational levels split into quartets with separation of up to hundreds of MHz between the torsional components, making the assignment of the microwave spectrum challenging. The present study on 26DMFB adds a contribution to the very limited number of investigations on C 2v molecules showing methyl internal rotations reported in the literature, which are acetone, [19] dimethyl ether, [20] diethyl ketone, [21] 2,5-dimethylfuran, [22] 2,5-dimethylthiophene, [23] and dimethyl sulfide. [24] 2.…”

Section: Introductionmentioning

confidence: 78%

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: Introductionmentioning

confidence: 78%

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

Khemissi

Nguyen

2020

ChemPhysChem

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“…Comparison between torsional barriers of oxygen and sulfur analogues has shown that the barrier height is always larger in the oxygen analogue, for example 2-methylfuran (413 cm 1 ) [31] vs. 2-methylthiophene (194 cm 1 ) [32] and dimethylfuran (439 cm 1 ) [33] vs. dimethylthiophene (248 cm 1 ) [34]. In a previous study on methyl propyl ether, only one conformer with Cs symmetry was observed where the barrier to internal rotation of the methoxy methyl group was determined to be 1154(21) cm 1 [35].…”

Section: Introductionmentioning

confidence: 99%

Laboratory rotational spectroscopy of methyl n-propyl sulfide: Conformational analysis and methyl internal rotation

Tulimat

Mouhib

Nguyen

et al. 2020

Journal of Molecular Spectroscopy

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The microwave spectra of methyl n-propyl sulfide, CH3-S-CH2-CH2-CH3, were recorded in the frequency region from 2.0 to 26.5 GHz, revealing three conformers. Quantum chemical calculations were carried out to support experimental work. Fine splittings arising from the internal rotation of the methyl group attached to the sulfur atom were resolved and analyzed. Torsional barriers of about 600 cm 1 for the two conformers with C1 symmetry and about 700 cm 1 for the Cs conformer could be deduced, showing that conformations affect the methyl internal rotation.Torsional splittings of the methyl group at the end of the propyl moiety were observed for some transitions, leading to the determination of barrier heights close to 1000 cm 1 . The spectrum of the 34 S isotopologue of the most stable conformer could be measured in natural abundance. The present laboratory work provides highly accurate spectroscopic parameters, which serve as reliable starting values for extrapolation in higher frequency ranges and for the search of this sulfur-containing molecule in the interstellar medium.

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“…Since decades, this is proven by the fact that many analysis methods have been developed to determine the three-dimensional structure of a molecule. Only a very limited number of microwave spectroscopic investigations on similar aromatic systems with two internal rotors are reported in the literature, e. g. 2,5-dimethylfurane, [5] 2,5-dimethylthiophene, [6] 2-acetyl-5-methylfuran, [7] and dimethylbenzaldehyde. In the gas phase, molecular jet Fourier transform microwave (FTMW) spectroscopy is the most suitable tool for this purpose.…”

Section: Introductionmentioning

confidence: 99%

Interplay Between Microwave Spectroscopy and X‐ray Diffraction: The Molecular Structure and Large Amplitude Motions of 2,3‐Dimethylanisole

et al. 2018

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To determine the structural properties of 2,3-dimethylanisole, a multidisciplinary approach was carried out where gas phase rotational spectroscopy recording a spectrum from 2 to 26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer was combined with solid-state X-ray diffraction. Both methods revealed that only one conformer with a planar heavy-atom structure exists. In the solid state, the packing in the monoclinic space group is P2 /n with Z=4. In the gas phase spectrum, torsional splittings due to the internal rotations of two methyl groups attached to the phenyl ring were resolved and analyzed, providing an estimate of the barriers to methyl internal rotation of V =26.9047(5) and 518.7(12) cm for the methyl groups at the ortho- and meta-position, respectively. The coupling between the two internal rotations is modeled on a two-dimensional potential energy surface, which was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory.

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The torsional barriers of two equivalent methyl internal rotations in 2,5-dimethylfuran investigated by microwave spectroscopy

Cited by 35 publications

References 28 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

Laboratory rotational spectroscopy of methyl n-propyl sulfide: Conformational analysis and methyl internal rotation

Interplay Between Microwave Spectroscopy and X‐ray Diffraction: The Molecular Structure and Large Amplitude Motions of 2,3‐Dimethylanisole

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