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Accurate conformational stability and cationic structure of piperidine determined by conformer-specific VUV-MATI spectroscopy

Title
Accurate conformational stability and cationic structure of piperidine determined by conformer-specific VUV-MATI spectroscopy
Authors
Eom S.Y.Lee Y.R.Kwon C.H.
Ewha Authors
이유란
SCOPUS Author ID
이유란scopus
Issue Date
2020
Journal Title
Physical Chemistry Chemical Physics
ISSN
1463-9076JCR Link
Citation
Physical Chemistry Chemical Physics vol. 22, no. 39, pp. 22823 - 22832
Publisher
Royal Society of Chemistry
Indexed
SCIE; SCOPUS WOS scopus
Document Type
Article
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). This journal is © the Owner Societies.
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DOI
10.1039/d0cp04407e
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자연과학대학 > 물리학전공 > Journal papers
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