Methyl rotors in the gas phase: A study of o- and m-toluidine by chirped-pulse Fourier transform microwave spectroscopy

Bird, Ryan G.; Pratt, David W.

doi:10.1016/j.jms.2011.03.002

Cited by 8 publications

(7 citation statements)

References 20 publications

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“…If only the nitrogen atom of the aromatic ring or a linear group of atoms such as the cyano group is in the neighborhood of the methyl rotor, then the torsional barriers are low, e.g., 90.3 cm −1 for α-picoline (1) [173,174], which is essentially the same as 94.4 cm −1 for 4methylpyrimidine (13) [185], while the value of 187.7 cm −1 for o-tolunitril (4) [177,178] is still rather low. The value increases tremendously to 525.5 cm −1 in thymine (15) [187], 531 cm −1 in o-toluidine (9) [182], and 686.3 cm −1 in o-nitrotoluene (6) [180]. These values are significantly higher than that of 444 cm −1 found for o-methylanisole (molecule (9) in Figure 5) [127].…”

Section: Nitrogen-containing Aromatic Six-membered Ringmentioning

confidence: 72%

“…We observe the same trend as in Figure 6, that the torsional barriers of the m-and p-isomers and, if induced by symmetry, V 6 potentials are very low. Interestingly, the V 6 potential of p-nitrotoluene (8) [180] is higher than the V 3 potential of the m-isomer (7) [181], and a surprisingly low V 3 barrier of only 2.0 cm −1 is found for m-toluidine (10) [182].…”

Section: Nitrogen-containing Aromatic Six-membered Ringmentioning

confidence: 89%

“…The investigations of monomethyl-substituted aromatic six-membered ring containing a nitrogen atom are limited to α-picoline [173,174], its N-oxide derivative [175], and 4picoline [176], the two isomers (ortho and meta) of tolunitril [177][178][179], as well as the three isomers of nitrotoluene [180,181] and toluidine [182,183]. This class of compounds also includes the methylpyrimidine family and thymine, in which the microwave spectra are significantly complicated by the presence of two nitrogen nuclei [184][185][186][187].…”

Section: Nitrogen-containing Aromatic Six-membered 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: Nitrogen-containing Aromatic Six-membered Ringmentioning

confidence: 72%

Section: Nitrogen-containing Aromatic Six-membered Ringmentioning

confidence: 89%

Section: Nitrogen-containing Aromatic Six-membered 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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“…Preliminary studies were carried out at the University of Pittsburgh using a miniaturized CP-FTMW spectrometer working in the 8-18 GHz range. 9 Subsequent studies utilized the 2-8 GHz CP-FTMW spectrometer at the University of Virginia. 10 In this case, two independent nozzles were used; each nozzle was heated to 90° C and the vaporized sample was seeded in a stream of Ne gas flowing at a backing pressure of 4 atm.…”

Section: Cis-cis (Ac)mentioning

confidence: 99%

N-ethylformamide dimer. A β-turn model peptide in the gas phase

Vaquero-Vara

Alstadt

Sewatsky

et al. 2017

Journal of Molecular Spectroscopy

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Reported here are CP-FTMW experiments on N-ethylformamide (NEF), previously studied by pure rotational spectroscopy in the gas phase by Hirota and co-workers [J. Mol. Struct. 744 (2005) 815-819]. Two conformers of the monomer (trans sc and cis ac), the trans-trans sc dimer, and several NEF-water complexes have been detected. (Only trans sc was observed in the earlier experiments.) Of these species, the trans-trans sc dimer is the most interesting since its three-dimensional structure bears a striking resemblance to β-turns in folded peptides. The well-known anti-parallel β-sheet structures would be expected to have near-zero dipole moments and are therefore discriminated against by the CP-FTMW method.

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“…There are currently four main spectral fitting and prediction programs for internal rotors in common use: BELGI [1], ERHAM [2], SPFIT (with IAMCALC) [3] and XIAM [4]. All of these programs have been used to handle a variety of systems from the centimeter-wave to the submillimeter-wave regions, and a few recent examples include hydroxyacetone [5], isopropenyl acetate [6], o-and m-toluidine [7], and two isomers of the hydrofluoroether C 4 F 9 OCH 3 [8]. Many of these programs have hard-coded limits on the maximum number of lines or maximum value of J, but these values can be easily extended through direct editing of the publicly-available source code [9,10].…”

Section: Introductionmentioning

confidence: 99%