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Sun H, Khemissi S, Kleiner I, Nguyen HVL. Low barriers to internal rotation in the microwave spectrum of 2,5-dimethylfluorobenzene. J Chem Phys 2024; 160:094302. [PMID: 38436444 DOI: 10.1063/5.0185005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2023] [Accepted: 01/24/2024] [Indexed: 03/05/2024] Open
Abstract
We investigated the rotational spectrum of 2,5-dimethylfluorobenzene containing coupled large amplitude motions of two methyl groups in the frequency range from 2 to 26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer. The internal rotation of two inequivalent methyl groups with low torsional barriers (around 16 and 226 cm-1) causes splittings of all rotational transitions into quintets with separations of up to hundreds of MHz between the torsional components. Spectral analysis and modeling of the observed splittings were performed using the programs XIAM and BELGI-Cs-2Tops, whereby the latter achieved measurement accuracy. The methyl internal rotation can be used to examine the electronic and steric environments around the methyl group because they affect the methyl torsional barrier. Electronic properties play a particularly important role in aromatic molecules in the presence of a π-conjugated double bond system. The experimental results were compared with those of quantum chemistry. Benchmark calculations resulted in the conclusion that the B3LYP-D3BJ/6-311++G(d,p) level of theory can be recommended for predicting rotational constants to guide the microwave spectral assignment of dimethylfluorobenzenes in particular and toluene derivatives in general.
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Affiliation(s)
- Haoyue Sun
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
| | - Safa Khemissi
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
- Institut Universitaire de France (IUF), F-75231 Paris, France
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Silva WGDP, Poonia T, van Wijngaarden J. Exploring the conformational landscape, hydrogen bonding, and internal dynamics in the diallyl ether and diallyl sulfide monohydrates. J Chem Phys 2024; 160:044302. [PMID: 38258923 DOI: 10.1063/5.0180901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 01/01/2024] [Indexed: 01/24/2024] Open
Abstract
The conformational spaces of the diallyl ether (DAE) and diallyl sulfide (DAS) monohydrates were explored using rotational spectroscopy from 6 to 19 GHz. Calculations at the B3LYP-D3(BJ)/aug-cc-pVTZ level suggested significant differences in their conformational behavior, with DAE-w exhibiting 22 unique conformers and DAS-w featuring three stable structures within 6 kJ mol-1. However, only transitions from the lowest energy conformer of each were experimentally observed. Spectral analysis confirmed that binding with water does not alter the conformational preference for the lowest energy structure of the monomers, but it does influence the relative stabilities of all other conformers, particularly in the case of DAE. Non-covalent interaction and quantum theory of atoms in molecules analyses showed that the observed conformer for each complex is stabilized by two intermolecular hydrogen bonds (HBs), where water primarily interacts with the central oxygen or sulfur atom of the diallyl compounds, along with secondary interactions involving the allyl groups. The nature of these interactions was further elucidated using symmetry-adapted perturbation theory, which suggests that the primary HB interaction with S in DAS is weaker and more dispersive in nature compared to the primary HB in DAE. This supports the experimental observation of a tunneling splitting exclusively in the rotational spectrum of DAS-w, as the weaker contact allows water to undergo internal motions within the complex, as shown based on calculated transition state structures for possible tunneling pathways.
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Affiliation(s)
- Weslley G D P Silva
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
- I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
| | - Tamanna Poonia
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
| | - Jennifer van Wijngaarden
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
- Department of Chemistry, York University, Toronto, Ontario M3J 1P3, Canada
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Khemissi S, Schwell M, Kleiner I, Nguyen HVL. Approaching the free rotor limit: extremely low methyl torsional barrier observed in the microwave spectrum of 2,4-dimethylfluorobenzene. Phys Chem Chem Phys 2023; 26:402-411. [PMID: 38078469 DOI: 10.1039/d3cp04748b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
The microwave spectrum of 2,4-dimethylfluorobenzene was recorded using a molecular jet Fourier transform microwave spectrometer in the frequency range from 2.0 to 26.5 GHz. The spectral assignment and modeling were challenging due to the large tunnelling splittings resulting from the very low barrier to internal rotation of the p-methyl group that approaches the free rotor limit. Internal rotation splittings arising from two inequivalent o- and p-methyl groups were observed, analysed and modelled using the modified version of the XIAM code and the BELGI-Cs-2Tops code, giving a root-mean-square deviation of 549.1 kHz and 4.5 kHz, respectively, for a data set of 885 rotational lines. The torsional barriers of the o- and p-methyl groups were determined to be 227.039(51) cm-1 and 3.23(40) cm-1, respectively. The V3 barrier observed for the p-methyl group is lower than in any other para-methyl substituted toluene derivatives with coupled internal rotations, becoming the lowest value ever observed to date. The barrier to internal rotation of the o-methyl group next to a fluorine atom is consistently around 220 cm-1, as confirmed by comparing it to barriers observed in other toluene derivatives. The experimental rotational constants were compared to those obtained by quantum chemical calculations.
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Affiliation(s)
- Safa Khemissi
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France.
| | - Martin Schwell
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France.
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France.
- Institut Universitaire de France (IUF), F-75231 Paris, France
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Xie F, Sun W, Hartwig B, Obenchain DA, Schnell M. Hydrogen-Atom Tunneling in a Homochiral Environment. Angew Chem Int Ed Engl 2023; 62:e202308273. [PMID: 37467465 DOI: 10.1002/anie.202308273] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 07/19/2023] [Accepted: 07/19/2023] [Indexed: 07/21/2023]
Abstract
The role-exchanging concerted torsional motion of two hydrogen atoms in the homochiral dimer of trans-1,2-cyclohexanediol was characterized through a combination of broadband rotational spectroscopy and theoretical modeling. The results reveal that the concerted tunneling motion of the hydrogen atoms leads to the inversion of the sign of the dipole moment components along the a and b principal axes, due to the interchange motion that cooperatively breaks and reforms one intermolecular hydrogen bond. This motion is also coupled with two acceptor switching motions. The energy difference between the two ground vibrational states arising from this tunneling motion was determined to be 29.003(2) MHz. The corresponding wavefunctions suggest that the two hydrogen atoms are evenly delocalized on two equivalent potential wells, which differs from the heterochiral case where the hydrogen atoms are confined in separate wells, as the permutation-inversion symmetry breaks down. This intriguing contrast in hydrogen-atom behavior between homochiral and heterochiral environments could further illuminate our understanding of the role of chirality in intermolecular interactions and dynamics.
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Affiliation(s)
- Fan Xie
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany
| | - Wenhao Sun
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany
| | - Beppo Hartwig
- Institut für Physikalische Chemie, Universität Göttingen, Tammannstr. 6, 37077, Göttingen, Germany
| | - Daniel A Obenchain
- Institut für Physikalische Chemie, Universität Göttingen, Tammannstr. 6, 37077, Göttingen, Germany
| | - Melanie Schnell
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 1, 24118, Kiel, Germany
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Baweja S, Antonelli E, Hussain S, Fernández-Ramos A, Kleiner I, Nguyen HVL, Sanz ME. Revealing Internal Rotation and 14N Nuclear Quadrupole Coupling in the Atmospheric Pollutant 4-Methyl-2-nitrophenol: Interplay of Microwave Spectroscopy and Quantum Chemical Calculations. Molecules 2023; 28:molecules28052153. [PMID: 36903397 PMCID: PMC10004196 DOI: 10.3390/molecules28052153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Revised: 02/17/2023] [Accepted: 02/17/2023] [Indexed: 03/02/2023] Open
Abstract
The structure and interactions of oxygenated aromatic molecules are of atmospheric interest due to their toxicity and as precursors of aerosols. Here, we present the analysis of 4-methyl-2-nitrophenol (4MNP) using chirped pulse and Fabry-Pérot Fourier transform microwave spectroscopy in combination with quantum chemical calculations. The rotational, centrifugal distortion, and 14N nuclear quadrupole coupling constants of the lowest-energy conformer of 4MNP were determined as well as the barrier to methyl internal rotation. The latter has a value of 106.4456(8) cm-1, significantly larger than those from related molecules with only one hydroxyl or nitro substituent in the same para or meta positions, respectively, as 4MNP. Our results serve as a basis to understand the interactions of 4MNP with atmospheric molecules and the influence of the electronic environment on methyl internal rotation barrier heights.
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Affiliation(s)
- Shefali Baweja
- Department of Chemistry, King’s College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Eleonore Antonelli
- Université Paris Est Créteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
| | - Safia Hussain
- Department of Chemistry, King’s College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
| | - Antonio Fernández-Ramos
- Departamento de Química Física and Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Jenaro de la Fuente s/n, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
| | - Isabelle Kleiner
- Université Paris Cité and Université Paris Est Créteil, CNRS, LISA, F-75013 Paris, France
| | - Ha Vinh Lam Nguyen
- Université Paris Est Créteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
- Institut Universitaire de France (IUF), 1 rue Descartes, F-75231 Paris, France
- Correspondence: (H.V.L.N.); (M.E.S.)
| | - M. Eugenia Sanz
- Department of Chemistry, King’s College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK
- Correspondence: (H.V.L.N.); (M.E.S.)
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