The low internal rotation barriers of halogenated toluenes: Rotational spectrum of 2,4-difluorotoluene

Nair, K. P. R.; Herbers, Sven; Obenchain, Daniel A.; Grabow, Jens‐Uwe; Lesarri, Alberto

doi:10.1016/j.jms.2017.10.003

Cited by 16 publications

(18 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Comparison of the methyl torsional barrier of two equivalent methyl groups in 26DMFB with the values of other toluene derivatives where the fluorine atom and the methyl group are adjacent. (1) 26DMFB (this work), (2) 2-fluorotoluene, [6] (3) 2,4,5-trifluorotoluene, [14] (4) 2,3,4trifluorotoluene, [14] (5) 2,3-difluorotoluene, [9] (6) 2,4-difluorotoluene, [10] (7) 2,5difluorotoluene, [11] and (8) 2,6-difluorotoluene. [13]…”

Section: Methodsmentioning

confidence: 69%

“…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%

See 1 more Smart Citation

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

Khemissi

Nguyen

2020

ChemPhysChem

View full text Add to dashboard Cite

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.

show abstract

Section: Methodsmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

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

Khemissi

Nguyen

2020

ChemPhysChem

View full text Add to dashboard Cite

show abstract

“…In the first member, 2,6-dimethylfluorobenzene (6), the internal rotations of two methyl tops are equivalent, resulting in splittings of all rotational transitions into quartets [32]. The torsional barrier of 236.7922(21) cm −1 reflects well the steric effect arising from a fluorine atom located next to the methyl groups, because similar values were found for 2-fluorotoluene (5) [21], n,m-difluorotoluene (n = 2, m = 3, 4, 5) [33][34][35], and 2,3,4and 2,4,5-trifluorotoluene [36]. Here, we report the results for the next member, 3,4dimethylfluorobenzene (34DMFB), where steric hindrance comes from two neighboring methyl tops.…”

Section: Introductionmentioning

confidence: 61%

Steric effects on two inequivalent methyl internal rotations of 3,4-dimethylfluorobenzene

Melan

Khemissi

Nguyen

2021

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

View full text Add to dashboard Cite

The microwave spectrum of 3,4-dimethylfluorobenzene was measured using a pulsed molecular jet Fourier transform microwave spectrometer operating in the frequency range from 2.0 to 26.5 GHz with the goal of quantifying the steric effects on the barriers to internal rotation of the two inequivalent methyl groups. Due to these torsional motions, splittings of all rotational transitions into quintets were observed and fitted with residuals close to measurement accuracy. The experimental work was supported by quantum chemical calculations, and the B3LYP-D3BJ/6-311++G(d,p) level of theory yielded accurate optimized geometry parameters to guide the assignment. The three-fold potential values of 456.19(13) cm −1 and 489.77(15) cm −1 for the methyl groups at the meta and para position, respectively, deduced from the experiments are compared with the predicted values and those of other toluene derivatives.

show abstract

“…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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

The low internal rotation barriers of halogenated toluenes: Rotational spectrum of 2,4-difluorotoluene

Cited by 16 publications

References 45 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

Steric effects on two inequivalent methyl internal rotations of 3,4-dimethylfluorobenzene

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

Contact Info

Product

Resources

About