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Non-oxidative photoreaction of 1,3,5-triaryl-2-pyrazoline-4-ol (4-methoxy) derivatives


Ebrahimi, Fatemeh; Memarian, Hamid Reza; Rudbari, Hadi Amiri; Blacque, Olivier (2023). Non-oxidative photoreaction of 1,3,5-triaryl-2-pyrazoline-4-ol (4-methoxy) derivatives. Journal of Photochemistry and Photobiology A: Chemistry, 435:114306.

Abstract

A series of 4-hydroxy- or 4-methoxy-substituted 1,3,5-triaryl-2-pyrazolines were synthesized and their structures, especially trans-orientation of 4- and 5-hydrogens of the 2-pyrazoline ring were characterized by analysis of IR, 1H NMR, 13C NMR spectra as well as the single-crystal structure study. In order to elucidate the effect of 4-hydroxy- or 4-methoxy-substitution on the photochemical behavior of these compounds, they were exposed to the UV light. The results explain the occurrence of a non-oxidative photoreaction, by the expulsion of 4-substitution and elimination of a molecule of water or methanol under the formation of the aromatized pyrazole ring. Density functional theory (DFT) calculations were carried out to support the proposed electron-transfer induced photoreaction mechanism. Natural bond orbital (NBO) analysis explains the preferred electron detachment process from the N1-atom rather than the oxygen atom of the hydroxy or the methoxy groups. Proton detachment from the involved radical cation species leads to the formation of the radical intermediate centered at the C5-position of the heterocyclic ring. Elimination of the hydroxy or the methoxy group accomplished the photoreaction under the formation of the C4-unsubstituted pyrazole molecule.

Abstract

A series of 4-hydroxy- or 4-methoxy-substituted 1,3,5-triaryl-2-pyrazolines were synthesized and their structures, especially trans-orientation of 4- and 5-hydrogens of the 2-pyrazoline ring were characterized by analysis of IR, 1H NMR, 13C NMR spectra as well as the single-crystal structure study. In order to elucidate the effect of 4-hydroxy- or 4-methoxy-substitution on the photochemical behavior of these compounds, they were exposed to the UV light. The results explain the occurrence of a non-oxidative photoreaction, by the expulsion of 4-substitution and elimination of a molecule of water or methanol under the formation of the aromatized pyrazole ring. Density functional theory (DFT) calculations were carried out to support the proposed electron-transfer induced photoreaction mechanism. Natural bond orbital (NBO) analysis explains the preferred electron detachment process from the N1-atom rather than the oxygen atom of the hydroxy or the methoxy groups. Proton detachment from the involved radical cation species leads to the formation of the radical intermediate centered at the C5-position of the heterocyclic ring. Elimination of the hydroxy or the methoxy group accomplished the photoreaction under the formation of the C4-unsubstituted pyrazole molecule.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > General Chemistry
Physical Sciences > General Chemical Engineering
Physical Sciences > General Physics and Astronomy
Uncontrolled Keywords:General Physics and Astronomy, General Chemical Engineering, General Chemistry
Language:English
Date:1 February 2023
Deposited On:09 Nov 2022 14:06
Last Modified:27 Feb 2024 02:48
Publisher:Elsevier
ISSN:1010-6030
OA Status:Closed
Publisher DOI:https://doi.org/10.1016/j.jphotochem.2022.114306