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Park SM, Kwon CH. Unraveling the Conformational Preference of Morpholine: Insights from Infrared Resonant Vacuum Ultraviolet Photoionization Mass Spectroscopy. J Phys Chem Lett 2023; 14:9472-9478. [PMID: 37831631 PMCID: PMC10615077 DOI: 10.1021/acs.jpclett.3c02280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Accepted: 09/27/2023] [Indexed: 10/15/2023]
Abstract
The preference for different conformations in morpholine has a notable effect on its behavior and reactivity in organic synthesis. Herein, we explored the intricate conformational properties of morpholines through a combination of advanced mass spectrometric techniques and theoretical calculations. Notably, we employed infrared (IR) resonant vacuum ultraviolet (VUV) mass-analyzed threshold ionization spectroscopy to measure the unique vibrational spectra of the distinct conformers (Chair-Eq and Chair-Ax) in morpholine for the first time. Through precise VUV photon energy adjustments to coincide with the vibrational excitation via IR absorption, we effectively pinpointed the adiabatic ionization thresholds corresponding to the Chair-Eq (65 442 ± 4 cm-1) and Chair-Ax (65 333 ± 4 cm-1) conformers. This allowed us to accurately determine the conformational stability between the two conformers (109 ± 4 cm-1). By shedding light on the conformational properties of morpholine, this study brings far-reaching implications to the fields of organic synthesis and pharmaceutical research.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry and
Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
| | - Chan Ho Kwon
- Department of Chemistry and
Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
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Li S, Zhao Y, Jiao Y, Zhao J, Li C, Jia S. Vibronic and Cationic Features of 2-Fluorobenzonitrile and 3-Fluorobenzonitrile Studied by REMPI and MATI Spectroscopy and Franck-Condon Simulations. Molecules 2023; 28:4702. [PMID: 37375257 DOI: 10.3390/molecules28124702] [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: 05/25/2023] [Revised: 06/08/2023] [Accepted: 06/09/2023] [Indexed: 06/29/2023] Open
Abstract
Fluorinated organic compounds have superior physicochemical properties than general organic compounds due to the strong C-F single bond; they are widely used in medicine, biology, pesticides, and materials science. In order to gain a deeper understanding of the physicochemical properties of fluorinated organic compounds, fluorinated aromatic compounds have been investigated by various spectroscopic techniques. 2-fluorobenzonitrile and 3-fluorobenzonitrile are important fine chemical intermediates and their excited state S1 and cationic ground state D0 vibrational features remain unknown. In this paper, we used two-color resonance two photon ionization (2-color REMPI) and mass analyzed threshold ionization (MATI) spectroscopy to study S1 and D0 state vibrational features of 2-fluorobenzonitrile and 3-fluorobenzonitrile. The precise excitation energy (band origin) and adiabatic ionization energy were determined to be 36,028 ± 2 cm-1 and 78,650 ± 5 cm-1 for 2-fluorobenzonitrile and 35,989 ± 2 cm-1 and 78,873 ± 5 cm-1 for 3-fluorobenzonitrile, respectively. The density functional theory (DFT) at the levels of RB3LYP/aug-cc-pvtz, TD-B3LYP/aug-cc-pvtz, and UB3LYP/aug-cc-pvtz were used to calculate the stable structures and vibrational frequencies for the ground state S0, excited state S1, and cationic ground state D0, respectively. Franck-Condon spectral simulations for transitions of S1 ← S0 and D0 ← S1 were performed based on the above DFT calculations. The theoretical and experimental results were in good agreement. The observed vibrational features in S1 and D0 states were assigned according to the simulated spectra and the comparison with structurally similar molecules. Several experimental findings and molecular features were discussed in detail.
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Affiliation(s)
- Shuxian Li
- State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
| | - Yan Zhao
- Department of Physics and Electronics Engineering, Jinzhong University, Jinzhong 030619, China
| | - Yuechun Jiao
- State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
| | - Jianming Zhao
- State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
| | - Changyong Li
- State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
| | - Suotang Jia
- State Key Laboratory of Quantum Optics and Quantum Optic Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
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Charvati E, Sun H. Potential Energy Surfaces Sampled in Cremer-Pople Coordinates and Represented by Common Force Field Functionals for Small Cyclic Molecules. J Phys Chem A 2023; 127:2646-2663. [PMID: 36893434 DOI: 10.1021/acs.jpca.3c00095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/11/2023]
Abstract
The complex conformations of the cyclic moieties impact the physical and chemical properties of molecules. In this work, we chose 22 molecules of four-, five-, and six-membered rings and performed a thorough conformational sampling using Cremer-Pople coordinates. With consideration of symmetries, we obtained a total of 1504 conformational structures for four-membered, 5576 for five-membered, and 13509 for six-membered rings. All well-known and many less well-known conformers for each molecule were identified. We represented the potential energy surfaces (PESs) by fitting the data to common analytical force field (FF) functional forms. We found that the general features of PESs can be described by the essential FF functional forms; however, the accuracy of representation can be improved remarkably by including the torsion-bond and torsion-angle coupling terms. The best fit yields R-squared (R2) values close to 1.0 and mean absolute errors in energy less than 0.3 kcal/mol.
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Affiliation(s)
- Evangelia Charvati
- School of Chemistry and Chemical Engineering, Materials Genome Initiative Center, and Key Laboratory of Scientific and Engineering Computing of Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Huai Sun
- School of Chemistry and Chemical Engineering, Materials Genome Initiative Center, and Key Laboratory of Scientific and Engineering Computing of Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240, China
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Conformational Structures of Neutral and Cationic Pivaldehyde Revealed by IR-Resonant VUV-MATI Mass Spectroscopy. Int J Mol Sci 2022; 23:ijms232314777. [PMID: 36499105 PMCID: PMC9735833 DOI: 10.3390/ijms232314777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 11/22/2022] [Accepted: 11/23/2022] [Indexed: 11/29/2022] Open
Abstract
Pivaldehyde, which is an unwanted by-product released with engine exhaust, has received considerable research attention because of its hydrocarbon oxidations at atmospheric temperature. To gain insight into the conformer-specific reaction dynamics, we investigated the conformational structures of the pivaldehyde molecule in neutral (S0) and cationic (D0) states using the recently invented IR-resonant VUV-MATI mass spectroscopy. Additionally, we constructed the two-dimensional potential energy surfaces (2D PESs) associated with the conformational transformations in the S0 and D0 states to deduce the conformations corresponding to the measured vibrational spectra. The 2D PESs indicated the presence of only the eclipsed conformation in the global minima of both states, unlike those in propanal and isobutanal. However, comparing the IR-dip VUV-MATI spectra from two intense peaks in the VUV-MATI spectrum with the anharmonic IR simulations revealed the correspondence between the gauche conformer on the S0 state and the measured IR spectra. Furthermore, Franck-Condon analysis confirmed that most peaks in the VUV-MATI spectrum are attributed to the adiabatic ionic transitions between the neutral gauche and cationic eclipsed conformers in pivaldehyde. Consequently, electron removal from the highest occupied molecular orbital, consisting of the nonbonding orbital of the oxygen atom in pivaldehyde, promoted the formyl-relevant modes in the induced cationic eclipsed conformer.
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Lee YR, Kwon CH. Determination of highest occupied molecular orbital and cationic structures of cyclopentanone using high‐resolution vacuum ultraviolet mass‐analyzed threshold ionization mass spectrophotometry. B KOREAN CHEM SOC 2022. [DOI: 10.1002/bkcs.12508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Yu Ran Lee
- Department Forensic Chemistry Division National Forensic Service Wonju Republic of Korea
| | - Chan Ho Kwon
- Department of Chemistry Kangwon National University Chuncheon Republic of Korea
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Fischer I, Pratt ST. Photoelectron spectroscopy in molecular physical chemistry. Phys Chem Chem Phys 2022; 24:1944-1959. [PMID: 35023533 DOI: 10.1039/d1cp04984d] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Photoelectron spectroscopy has long been a powerful method in the toolbox of experimental physical chemistry and molecular physics. Recent improvements in coincidence methods, charged-particle imaging, and electron energy resolution have greatly expanded the variety of environments in which photoelectron spectroscopy can be applied, as well as the range of questions that can now be addressed. In this Perspectives Article, we focus on selected recent studies that highlight these advances and research areas. The topics include reactive intermediates and new thermochemical data, high-resolution comparisons of experiment and theory using methods based on pulsed-field ionisation (PFI), and the application of photoelectron spectroscopy as an analytical tool to monitor chemical reactions in complex environments, like model flames, catalytic or high-temperature reactors.
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Affiliation(s)
- Ingo Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
| | - Stephen T Pratt
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA.
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Park SM, Kwon CH. Identification of individual conformers in C 4H 6O isomers using conformer-specific vibrational spectroscopy. RSC Adv 2021; 11:38240-38246. [PMID: 35498109 PMCID: PMC9044234 DOI: 10.1039/d1ra07397d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Accepted: 11/23/2021] [Indexed: 11/21/2022] Open
Abstract
We measured the conformer-specific vibrational spectra of C4H6O isomers in neutral and cationic states using IR resonant vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy for the first time. Notably, the measured IR dip and hole-burn VUV-MATI spectra for each isomer represent the identifiable vibrational spectra of individual conformers in both states. Furthermore, we estimated the relative populations of individual conformers in crotonaldehyde (CA) and methyl vinyl ketone (MVK) isomers using the IR dip intensity, the corresponding Franck-Condon factor, and the IR absorption cross section. Our analysis revealed that the compositional ratio of s-trans to s-cis conformers in the CA isomer remained at 95.8 : 4.2 even under supersonic expansion, whereas that in the MVK isomer was determined as 90.6 : 9.4, which is consistent with previous research. These findings reveal that the conformational stability of each isomer depends on the position of the methyl group relative to the carbonyl group.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University Chuncheon 24341 Korea
| | - Chan Ho Kwon
- Department of Chemistry, Institute for Molecular Science and Fusion Technology, Kangwon National University Chuncheon 24341 Korea
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Park SM, Kwon CH. Development and Verification of Conformer-Specific Vibrational Spectroscopy. J Phys Chem A 2021; 125:9251-9258. [PMID: 34628860 DOI: 10.1021/acs.jpca.1c07162] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Conformers have similar vibrational structures both in neutral (S0) and cationic (D0) states owing to the comparable force fields between their nuclei. Nevertheless, there is a continuous development of vibrational spectroscopic techniques to rigorously identify individual conformers in the designated molecule but only in the S0 state. We developed an inventive conformer-specific vibrational spectroscopic technique to measure identifiable vibrational spectra of individual conformers in both S0 and D0 states. We measured isomer-specific vibrational spectra in both states for gas-phase acetone and oxetane isomers from a solution with azeotropic composition to verify the proposed techniques that are based on infrared (IR) resonant vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. The measured IR dip VUV-MATI and IR hole-burn VUV-MATI spectra for each isomer, which correspond to isomer-specific vibrational spectra in both states, can be represented by IR-resonant VUV photoionization and one-photon VUV-MATI spectra of the binary mixture, respectively, under supersonic expansion conditions. The partial pressures of the individual isomers in the binary mixture with different mole fractions estimated according to the relative peak intensities in the measured spectra provide insights on solute-solvent interactions. We suggest that the verified IR-resonant VUV-MATI spectroscopy can form the basis of effective schemes toward conformational chemistry.
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Affiliation(s)
- Sung Man Park
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea
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