Structure and methyl torsion of halogenated toluenes: Rotational spectrum of 3,4-difluorotoluene

Nair, K. P. R.; Herbers, Sven; Grabow, Jens‐Uwe

doi:10.1016/j.jms.2018.11.007

Cited by 10 publications

(21 citation statements)

References 34 publications

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“…The arbitrary intensity is given in a logarithmic scale. The (01) torsional component is the strongest, followed by the (00) component, while the(11) and(12) species are weakest, in agreement with the spin statistical weight.…”

supporting

confidence: 71%

“…Especially for spectroscopy, the rotational spectrum of toluene has always attracted attention since its microwave spectrum was recorded and analyzed for the first time by Rudolph et al [1] Not only the structure of toluene was determined to great accuracy, several theoretical models and program codes have been also developed to reproduce the V 6 potential arising from the internal rotation of the C 3v methyl group attached to a phenyl frame with C 2v symmetry. [2][3][4][5] To gain insights into the substitution effect on this large amplitude motion (LAM) of toluene, studies on many fluorinated derivatives have been performed, such as the investigations on three isomers of fluorotoluene, [6][7][8] a systematic microwave investigation on the six isomers of difluorotoluene, [9][10][11][12][13] and the work on two isomers of trifluorotoluene. [14] All these studies have shown a variety of the potentials of the methyl torsion in both shape and height, which depend on the substituted position(s) of the fluorine atom(s).…”

Section: Introductionmentioning

confidence: 99%

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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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supporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

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

Khemissi

Nguyen

2020

ChemPhysChem

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“…The determination of the internal rotation barriers offers insight into the changes in the electronic structure of toluene caused by the substituent effects. A vast number of fluoro substituted toluenes have been investigated, such as the three isomers of fluorotoluene [1][2][3][4], the six isomers of difluorotoluene [5][6][7][8][9], and 2,6-dimethylfluorobenzene [10], but studies on chloro-substituted toluenes are rather scarce. The reason is probably the quadrupole moment of the chlorine nucleus coupling the nuclear spin I = 3/2 to the end-over-end rotation of the molecule, thereby causing a hyperfine structure (hfs) in addition to the methyl torsional splittings.…”

Section: Introductionmentioning

confidence: 99%

Internal rotation and chlorine nuclear quadrupole coupling in 2-chloro-4-fluorotoluene explored by microwave spectroscopy and quantum chemistry

Nair

Herbers

Bailey

et al. 2021

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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2-Chloro-4-fluorotoluene was investigated using a combination of molecular jet Fourier transform microwave spectroscopy in the frequency range from 5 to 21 GHz and quantum chemistry. The molecule experiences an internal rotation of the methyl group, which causes a fine splitting of all rotational transitions into doublets with separation on the order of a few tens of kHz. In addition, hyperfine effects originating from the chlorine nuclear quadrupole moment coupling its spin to the end-over-end rotation of the molecule are observed. The torsional barrier was derived using both the rho and the combined-axis-method, giving a value of 462.5(41) cm -1 . Accurate rotational constants and quadrupole coupling constants were determined for two 35 Cl and 37 Cl isotopologues and compared with Bailey's semi-experimental quantum chemical predictions. The gas phase molecular structure was deduced from the experimental rotational constants supplemented with those calculated by quantum chemistry at various levels of theory. The values of the methyl torsional barrier and chlorine nuclear quadrupole coupling constants were compared with the theoretical predictions and with those of other chlorotoluene derivatives.

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“…While it is the electron density for DFT, the wave function is optimized by MP2. If the molecule belongs to a systematic investigation on a molecular class, a certain level of theory is often preferred, which has yielded more reliable results in previous studies [70]. Otherwise, MP2 is usually recommended and represents one of the most favorable methods in the microwave spectroscopic community because of the reasonable rate between accuracy and required computational time.…”

Section: Methods Choice: Be Careful Discrepancy!mentioning

confidence: 99%

Understanding (coupled) large amplitude motions: the interplay of microwave spectroscopy, spectral modeling, and quantum chemistry

Nguyen

Kleiner

2020

Physical Sciences Reviews

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A large variety of molecules contain large amplitude motions (LAMs), inter alia internal rotation and inversion tunneling, resulting in tunneling splittings in their rotational spectrum. We will present the modern strategy to study LAMs using a combination of molecular jet Fourier transform microwave spectroscopy, spectral modeling, and quantum chemical calculations to characterize such systems by the analysis of their rotational spectra. This interplay is particularly successful in decoding complex spectra revealing LAMs and providing reference data for fundamental physics, astrochemistry, atmospheric/environmental chemistry and analytics, or fundamental researches in physical chemistry. Addressing experimental key aspects, a brief presentation on the two most popular types of state-of-the-art Fourier transform microwave spectrometer technology, i.e., pulsed supersonic jet expansion–based spectrometers employing narrow-band pulse or broad-band chirp excitation, will be given first. Secondly, the use of quantum chemistry as a supporting tool for rotational spectroscopy will be discussed with emphasis on conformational analysis. Several computer codes for fitting rotational spectra exhibiting fine structure arising from LAMs are discussed with their advantages and drawbacks. Furthermore, a number of examples will provide an overview on the wealth of information that can be drawn from the rotational spectra, leading to new insights into the molecular structure and dynamics. The focus will be on the interpretation of potential barriers and how LAMs can act as sensors within molecules to help us understand the molecular behavior in the laboratory and nature.

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Structure and methyl torsion of halogenated toluenes: Rotational spectrum of 3,4-difluorotoluene

Cited by 10 publications

References 34 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 and chlorine nuclear quadrupole coupling in 2-chloro-4-fluorotoluene explored by microwave spectroscopy and quantum chemistry

Understanding (coupled) large amplitude motions: the interplay of microwave spectroscopy, spectral modeling, and quantum chemistry

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