Large amplitude inversion tunneling motion in ammonia, methylamine, hydrazine, and secondary amines: From structure determination to coordination chemistry

Nguyen, Ha Vinh Lam; Gulaczyk, Iwona; Krȩglewski, Marek; Kleiner, Isabelle

doi:10.1016/j.ccr.2021.213797

Cited by 19 publications

(19 citation statements)

References 226 publications

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“…Large Amplitude Motion (LAM) has been a classic topic in microwave spectroscopy along its whole history over the last several decades. [1][2][3] Among them, the most extensively studied LAM is probably the internal rotation of methyl groups. The spectral feature includes torsional fine structures and is significantly more complicated than that of a simple rigid-rotor molecule.…”

Section: Introductionmentioning

confidence: 99%

Microwave Spectrum of Two‐Top Molecule: 2‐Acetyl‐3‐Methylthiophene

Dindić

Nguyen

2021

ChemPhysChem

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The microwave spectrum of 2-acetyl-3-methylthiophene (2A3MT) was recorded in the frequency range from 2 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer and could be fully assigned to the anti-conformer of the molecule, while the syn-conformer was not observable. Torsional splittings of all rotational transitions in quintets due to internal rotations of the acetyl methyl and the ring methyl groups were resolved and analyzed, yielding barriers to internal rotation of 306.184(46) cm À 1 and 321.813(64) cm À 1 , respectively. The rotational and centrifugal distortion constants were determined with high accuracy, and the experimental values are compared to those derived from quantum chemical calculations. The experimentally determined inertial defect supports the conclusion that anti-2A3MT is planar, even though a number of MP2 calculations predicted the contrary.

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Section: Introductionmentioning

confidence: 99%

Microwave Spectrum of Two‐Top Molecule: 2‐Acetyl‐3‐Methylthiophene

Dindić

Nguyen

2021

ChemPhysChem

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“…While comparing the value of the V 3 potential obtained for 25DMP with that of 2-methylpyrrole 46 and those of other five-membered rings, as given in Fig. 5, we found that for 2-and 2,5-methylated heterocyclic rings, the barrier to internal rotation is lowest in mono-methylated and di-methylated thiophenes (1, 2), higher in substituted pyrroles (3,4), and highest in substituted furans (5,6). The same holds true when comparing mono-methylated thiazoles, imidazoles, and oxazoles.…”

Section: Discussionmentioning

confidence: 83%

“…Besides the classic topics in structural chemistry, 1 large amplitude motions (LAMs), e.g., internal rotation, 2 ring puckering, 3 and inversion motion, 4 form a very active area in microwave spectroscopy. The effect of a methyl internal rotation on the rotational spectrum is that each rotational transition exhibits a torsional fine structure caused by the interaction of the methyl internal and the overall rotation.…”

Section: Introductionmentioning

confidence: 99%

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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“…Microwave spectroscopy is classically connected with the topic of structural chemistry, because the primary parameters deduced from a microwave spectrum, the rotational constants, directly reflect the mass distribution of the atoms in the molecule [1]. However, along the history of almost one century since the first microwave spectrum of ammonia was measured in 1934 [2], large amplitude motions (LAMs) have been involved, either in the form of inversion motion [3], ring puckering [4], or internal rotation [5]. If the molecule features a methyl group undergoing internal rotation, a torsional fine structure consisting of A-E doublets can be observed.…”

Section: Introductionmentioning

confidence: 99%