14N nuclear quadrupole coupling and methyl internal rotation in 3-methylpyrrole investigated by microwave spectroscopy

Nguyen, Thuy Ngoc; Stahl, Wolfgang; Nguyen, Ha Vinh Lam; Kleiner, Isabelle

doi:10.1016/j.jms.2020.111351

Cited by 10 publications

(13 citation statements)

References 33 publications

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“…Several classes of monomethyl-substituted planar five-membered rings have been reported in the literature as summarized in Figure 3. 16) 5-methylisoxazole [109], (17) Nmethylpyrrole [111], (18) 2-methylpyrrole [112], (19) 3-methylpyrrole [113], (20) N-methylimidazole [114], (21) 2-methylimidazole [114], (22) 4-methylimidazole [114], (23) 5-methylimidazole [114], (24) methyl furazan [115], (25) N-methylpyrazole [116].…”

Section: Sole Methyl Substitution On the Ringmentioning

confidence: 99%

“…In the class of methylpyrrole, the potential of N-methylpyrrole (17) possesses a pure V 6 term with a barrier of about 60 cm −1 [111]. The C 2v symmetry is broken in the cases of 2-(18) and 3-methylpyrrole (19), leading to V 3 potentials of 280 cm −1 [112] and 246 cm −1 [113], respectively, without significant V 6 contributions. In methylimidazole, the symmetry is also broken in the case of the N-isomer (20) due to the presence of an additional nitrogen atom at the third position of the ring, and only V 3 potentials were reported for all four isomers of this class [114].…”

Section: Sole Methyl Substitution On the Ringmentioning

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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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: Sole Methyl Substitution On the Ringmentioning

confidence: 99%

Section: Sole Methyl Substitution On the Ringmentioning

confidence: 99%

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

2022

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“…The same holds true when comparing mono-methylated thiazoles, imidazoles, and oxazoles. 56 We also observe that the barrier is always This is the author's peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.…”

Section: Discussionmentioning

confidence: 74%

Local vs global approaches to treat two equivalent methyl internal rotations and 14N nuclear quadrupole coupling of 2,5-dimethylpyrrole

Nguyen

Stahl

Nguyen

et al. 2021

The Journal of Chemical Physics

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The microwave spectrum of 2,5-dimethylpyrrole was recorded using a molecular jet Fourier transform microwave spectrometer operating in the frequency range from 2 to 26.5 GHz. Only one stable conformer was observed as expected and confirmed by quantum chemical calculations carried out to complement the experimental analysis.The two equivalent methyl groups cause each rotational transition to split into four torsional species, which is combined with the quadrupole hyperfine splittings in the same order of magnitude arising from the 14 N nucleus.This results in a complicated spectrum feature. The spectral assignment was done separately for each torsional species. Two global fits were carried out using the XIAM code and the BELGI-C 2v -2Tops-hyperfine code, a modified version of the BELGI-C 2v -2Tops code, giving satisfactory root-mean-square deviations. The potential barriers to internal rotation of the two methyl groups were determined to be V 3 = 317.208( 16) cm −1 . The molecular parameters were obtained with high accuracy, providing all necessary ground state information for further investigations in higher frequency ranges and on excited torsional-vibrational states.

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“…The internal rotation potential and particularly the

parameter is sensitive to both steric and electronic effects. In heterocyclic compounds, electronic effects are usually dominant [ 32 , 34 ]. When we compare the

values of the three heterocyclic compounds, we can observe that: first, the variation of

is stronger when the methyl group is substituted to the second position (2-MF, 2-MT and 2-MP) compared to its third position (3-MF, 3-MT and 3-MP); second,

is larger for MF compared to MT and MP (

for the 2- position and

for the 3- isomers) since a larger electro-negativity of the oxygen which creates an electronic environment hindering the internal methyl rotation.…”

Section: Discussionmentioning

confidence: 99%

“…Based on DFT calculations, these (

) parameters are discussed considering other sulfur and nitrogen heterocyclic analog in order to better understand the influence of the electronic environment on the internal rotation barrier and its higher-order correction term. To confirm experimentally the identified trends, we propose to investigate in the mm-wave domain the rotational-torsional spectroscopy of MP and MT already studied in the microwave domain [ 31 , 32 , 33 , 34 ]. Finally, in order to assign the remaining mm-wave lines of 2-MF and 3-MF, a rovibrational analysis of the lowest energy vibrational modes will be undertaken by means of synchrotron-based FT-Far-IR high-resolution spectroscopy as it was done recently by our group on the catechol molecule [ 15 ].…”

Section: Discussionmentioning

confidence: 99%

Millimeter-Wave Spectroscopy of Methylfuran Isomers: Local vs. Global Treatments of the Internal Rotation

et al. 2022

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Methylfurans are methylated aromatic heterocyclic volatile organic compounds and primary or secondary pollutants in the atmosphere due to their capability to form secondary organic aerosols in presence of atmospheric oxidants. There is therefore a significant interest to monitor these molecules in the gas phase. High resolution spectroscopic studies of methylated furan compounds are generally limited to pure rotational spectroscopy in the vibrational ground state. This lack of results might be explained by the difficulties arisen from the internal rotation of the methyl group inducing non-trivial patterns in the rotational spectra. In this study, we discuss the benefits to assign the mm-wave rotational-torsional spectra of methylfuran with the global approach of the BELGI-Cs code compared to local approaches such as XIAM and ERHAM. The global approach reproduces the observed rotational lines of 2-methylfuran and 3-methylfuran in the mm-wave region at the experimental accuracy for the ground vt=0 and the first torsional vt=1 states with a unique set of molecular parameters. In addition, the V3 and V6 parameters describing the internal rotation potential barrier may be determined with a high degree of accuracy with the global approach. Finally, a discussion with other heterocyclic compounds enables the study of the influence of the electronic environment on the hindered rotation of the methyl group.

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14N nuclear quadrupole coupling and methyl internal rotation in 3-methylpyrrole investigated by microwave spectroscopy

Cited by 10 publications

References 33 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

Local vs global approaches to treat two equivalent methyl internal rotations and 14N nuclear quadrupole coupling of 2,5-dimethylpyrrole

Millimeter-Wave Spectroscopy of Methylfuran Isomers: Local vs. Global Treatments of the Internal Rotation

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