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Park SM, Kwon CH. Deciphering the conformational preference and ionization dynamics of tetrahydrofuran: Insights from advanced spectroscopic techniques. J Chem Phys 2024; 160:114308. [PMID: 38497473 DOI: 10.1063/5.0186570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Accepted: 03/04/2024] [Indexed: 03/19/2024] Open
Abstract
Tetrahydrofuran (THF) has garnered significant attention due to its pivotal role in biological and chemical processes. The diverse array of conformations exhibited by THF profoundly impacts its reactivity and interactions with other molecules. Understanding these conformational preferences is crucial for comprehending its molecular behavior. In this study, we utilize infrared (IR) resonant vacuum ultraviolet photoionization/mass-analyzed threshold ionization (VUV-PI/MATI) mass spectroscopies to capture distinctive vibrational spectra of individual conformers, namely, "twisted" and "bent," within THF. Our conformer-specific vibrational spectra provide valuable insights into the relative populations of these two conformers. The analysis reveals that the twisted (C2) conformer is more stable than the bent (CS) conformer by 17 ± 15 cm-1. By precisely tuning the VUV photon energy to coincide with vibrational excitation via IR absorption, we selectively ionize specific conformers, yielding two-photon IR + VUV-PI/MATI spectra corresponding to the twisted and bent conformers. This investigation conclusively affirms that both the twisted and bent conformers coexist in the neutral state, while only the twisted conformer exists in the cationic state. These findings not only bridge gaps in existing knowledge but also provide profound insights into the behavior of this pivotal molecule in the realms of biology and medicine.
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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, Republic of Korea
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Republic of Korea
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2
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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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3
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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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Lee YR, Kwon CH. Innovative mass spectrometer for high-resolution ion spectroscopy. J Chem Phys 2021; 155:164203. [PMID: 34717366 DOI: 10.1063/5.0066348] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Conventional ion spectroscopy is inapplicable for ions produced in low concentrations or with low spectral resolutions. Hence, we constructed a high-resolution vacuum ultraviolet mass-analyzed threshold ionization (HR VUV-MATI) spectrometer composed of a four-wave frequency mixing cell capable of generating long-lasting and intense VUV laser pulses of ∼1 × 1010 photons/pulse at wavelengths of 123.6-160.0 nm, a space-focused linear time-of-flight photoionization chamber with a new ion-source assembly, and a compact molecular beam chamber with a temperature-controlled pulsed nozzle for ion spectroscopy. The ion-source assembly and pulsing schemes enabled an ∼15-μs-delayed but extremely weak pulsed-field-ionization of the molecules in the zero-kinetic-energy (ZEKE) states and first-order space focusing of the generated MATI ions. These ZEKE states were effectively generated by a minute electric jitter from the high-lying Rydberg states, which were initially prepared via VUV photoexcitation. The spectral and mass resolutions (∼5 cm-1 and 2400, respectively) and the signal strength were simultaneously enhanced using this spectrometer. Moreover, it could be used to measure the fine vibrational spectrum from the zero-point level of the cation and the exact adiabatic ionization energy of the neutral molecule. Additionally, it could be used to measure the appearance energies of the photoproducts and elucidate the vibrational structures of the cationic isotopomers, utilizing other pulsing schemes. Furthermore, this spectrometer could be used to analyze the congested vibrational spectrum of a cation with multiple conformations. Thus, the HR VUV-MATI spectrometer-a potential alternative to photoelectron spectrometers-can be used to analyze the conformational structure-dependent reactivities.
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Affiliation(s)
- Yu Ran Lee
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Republic of Korea
| | - Chan Ho Kwon
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Republic of Korea
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Lee YR, Kim MH, Kwon CH. Probing the Photoionization Dynamics of 2-Cyclopenten-1-one via High-Resolution VUV-MATI Spectroscopy. J Phys Chem A 2021; 125:2356-2363. [PMID: 33724025 DOI: 10.1021/acs.jpca.1c01093] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
2-Cyclopenten-1-one (2CP), which is a cyclic enone, has been considered an important precursor because of its versatile functionality in the synthesis of natural products and materials for biofuels. Here, we report the adiabatic ionization energy (AIE) and cationic structure of 2CP in the ionic transition between the neutral S0 and the cationic D0 states probed by high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. From the 0-0 band position in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the AIE of 2CP was determined to be 9.3477 ± 0.0004 eV (75,395 ± 3 cm-1), which is in good agreement with the reference value but much more accurate. The measured MATI spectrum combined with the Franck-Condon fitting at the B3LYP/cc-pVTZ level revealed that the cationic structure of 2CP is twisted with the C1 symmetry, whereas the neutral 2CP has the CS symmetry. The results indicate that geometrical changes induced by ionization are mainly attributed to the electron removal from the highest occupied molecular orbital, which consists of nonbonding orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane of 2CP. Consequently, lowering the C1 symmetry for cationic 2CP led to the promotions of the ring-bending and ring-twisting modes in the MATI spectrum, which correspond to the ring puckering and C═C twisting in the S0 state, respectively.
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Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center, Ewha Womans University, Seoul 03760, South Korea
| | - Myung Hwa Kim
- Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 03760, South Korea
| | - Chan Ho Kwon
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
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Park SM, Choi J, Kim HL, Kwon CH. Conformer-specific VUV-MATI spectroscopy of methyl vinyl ketone: stabilities and cationic structures of the s- trans and s- cis conformers. Phys Chem Chem Phys 2020; 22:28383-28392. [PMID: 33300923 DOI: 10.1039/d0cp05782g] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Methyl vinyl ketone (MVK), a volatile compound with photochemical activity, has received considerable attention in the fields of environmental chemistry and atmospheric chemistry. We explored the conformational stabilities of MVK in the neutral S0 and the cationic D0 states using conformer-specific vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy, which provided identifiable vibrational spectra for cationic MVK conformers. Based on the origin bands of the two individual conformers of MVK identified in the MATI spectra under different supersonic expansion conditions, the accurate adiabatic ionization energies of the s-trans and the s-cis conformers were determined to be 77 867 ± 4 (9.6543 ± 0.0005 eV) and 78 222 ± 4 cm-1 (9.6983 ± 0.0005 eV), respectively. The identifiable vibrational spectra of the two cationic conformers were further confirmed using vibrational assignments based on the Franck-Condon fit. Accordingly, precise cationic structures of the MVK conformers could be determined. The structural changes of the two conformers upon ionization could be attributed to the removal of an electron from the highest occupied molecular orbital of each conformer, which consists of nonbonding molecular orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane. Consequently, the s-trans conformer was preferred by 48 ± 18 and 403 ± 18 cm-1 in the neutral ground S0 and the cationic D0 states, respectively, which was supported by density-corrected density functional theory calculations and natural bond orbital analysis.
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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.
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Kang DW, Yoon DK, Kwon CH. Conformational potential energy surfaces and cationic structure of 3,4-dihydro-2 H-pyran by VUV-MATI spectroscopy and Franck-Condon fitting. Phys Chem Chem Phys 2020; 22:27673-27680. [PMID: 33236742 DOI: 10.1039/d0cp05193d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ring conformations of 3,4-dihydro-2H-pyran (34DHP) have attracted considerable interest owing to their structural similarity to cyclohexene, an important molecule in stereochemistry. In this study, we investigated the conformational interconversion of 34DHP in both the neutral (S0) and the cationic (D0) ground states. High-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy was utilized to obtain information regarding the adiabatic ionic transition between the S0 and the D0 states. Based on the 0-0 band in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the adiabatic ionization energy of 34DHP was accurately determined to be 8.3355 ± 0.0005 eV (67 230 ± 4 cm-1). To identify the conformer corresponding to this measured value, two-dimensional potential energy surfaces (2D PESs) associated with conformational interconversion in the S0 and the D0 states were constructed at the B3LYP/aug-cc-pVTZ level. It was revealed that in the S0 state, the twisted conformers undergo interconversion through the asymmetric bent conformation on the pseudorotational pathway, whereas in the D0 state, the half-bent conformers directly undergo interconversion via the planar conformation at the saddle point of 2D PES. The change in the conformational interconversion pathway upon ionization is attributed to electron removal from the highest occupied molecular orbital, which consists of a π orbital in the 2C-3C double bond interacting with a nonbonding orbital in the oxygen atom of 34DHP. Then, vibrational assignment of the observed spectrum could be achieved through Franck-Condon fitting for ionic transitions between the neutral twisted and the cationic half-bent conformers. The strong promotion of the ring bending and the 1O-2C-3C asymmetric stretching modes in the adiabatic ionic transitions confirmed the determined cationic structure of 34DHP.
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Affiliation(s)
- Do Won Kang
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
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Eom SY, Lee YR, Kwon CH. Accurate conformational stability and cationic structure of piperidine determined by conformer-specific VUV-MATI spectroscopy. Phys Chem Chem Phys 2020; 22:22823-22832. [PMID: 33021609 DOI: 10.1039/d0cp04407e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Piperidine has received attention in pharmaceutical synthesis and biochemical degradation because of its conformational activity. We explored the conformational structures of piperidine in the neutral (S0) and cationic (D0) ground states by conformer-specific vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy, which provides high-resolution vibrational spectra for the corresponding cationic conformer. To identify conformers corresponding to the obtained VUV-MATI spectra, equilibrium structures of piperidine conformers in the S0 and D0 states were determined at various density functional theory levels, and potential energy surfaces associated with the conformational changes were constructed. Notably, the chair form interconverting between the equatorial NH and the axial NH conformers (Chair-Eq and Chair-Ax) in piperidine lies on the global minimum of the S0 state, but only the axial-like NH conformer (Chair-Ax-like) in chair form exists in the D0 state. The vibrational assignment of the observed spectra was accomplished through Franck-Condon (FC) analysis for adiabatic transitions between two Chair-Eq and Chair-Ax conformers and a cationic Chair-Ax-like conformer. Rigorous FC analysis revealed the precise structure of a cationic Chair-Ax-like conformer induced by removal of an electron from the lone-pair sp3 orbital of the nitrogen atom in piperidine. The adiabatic ionization energies of Chair-Eq and Chair-Ax conformers converting to a cationic state were determined to be 64 704 ± 4 cm-1 (8.0223 ± 0.0005 eV) and 64 473 ± 4 cm-1 (7.9936 ± 0.0005 eV), respectively. Consequently, the difference between their adiabatic ionization energies allowed the accurate determination of the conformational stability of Chair-Eq and Chair-Ax conformers in piperidine (231 ± 4 cm-1).
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Affiliation(s)
- So Young Eom
- Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
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Lee YR, Choi N, Kwon CH. Determination of the highest occupied molecular orbital and cationic structure of 2-chloropyridine by one-photon VUV-MATI spectroscopy and Franck–Condon fitting. Phys Chem Chem Phys 2020; 22:20858-20866. [DOI: 10.1039/d0cp03365k] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Substitution of a chlorine atom for the H in pyridine alters the HOMO of the molecule, which ultimately affects the cationic structure.
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Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center
- Ewha Womans University
- Seoul 03760
- Korea
| | - Nayoung Choi
- 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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Lee YR, Kim HL, Kwon CH. Determination of the cationic conformational structure of tetrahydrothiophene by one-photon MATI spectroscopy and Franck–Condon fitting. Phys Chem Chem Phys 2020; 22:6184-6191. [DOI: 10.1039/d0cp00073f] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This study affords more accurate information regarding the pseudorotational PES describing the conformational interconversion of THT.
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Affiliation(s)
- Yu Ran Lee
- Department of Chemistry and Institute for Molecular Science and Fusion Technology
- Kangwon National University
- Chuncheon 24341
- Korea
| | - Hong Lae Kim
- 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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Lee YR, Kim MH, Kwon CH. Ring opening dissociation of cationic twisted conformer by conformer-specific cyclopentanone photoionization. J Chem Phys 2019; 151:164305. [DOI: 10.1063/1.5127233] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yu Ran Lee
- New and Renewable Energy Research Center, Ewha Womans University, Seoul 03760, South Korea
| | - Myung Hwa Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, South Korea
| | - Chan Ho Kwon
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
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