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Roque JPL, Rosado MTS, Fausto R, Reva I. Dual Photochemistry of Benzimidazole. J Org Chem 2023; 88:2884-2897. [PMID: 36795993 PMCID: PMC9990075 DOI: 10.1021/acs.joc.2c02560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Monomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were identified as 4H- and 6H-tautomers. Simultaneously, a family of photoproducts bearing the isocyano moiety was identified. Thereby, the photochemistry of benzimidazole was hypothesized to follow two reaction pathways: the fixed-ring and the ring-opening isomerizations. The former reaction channel results in the cleavage of the NH bond and formation of a benzimidazolyl radical and an H-atom. The latter reaction channel involves the cleavage of the five-membered ring and concomitant shift of the H-atom from the CH bond of the imidazole moiety to the neighboring NH group, leading to 2-isocyanoaniline and subsequently to the isocyanoanilinyl radical. The mechanistic analysis of the observed photochemistry suggests that detached H-atoms, in both cases, recombine with the benzimidazolyl or isocyanoanilinyl radicals, predominantly at the positions with the largest spin density (revealed using the natural bond analysis computations). The photochemistry of benzimidazole therefore occupies an intermediate position between the earlier studied prototype cases of indole and benzoxazole, which exhibit exclusively the fixed-ring and the ring-opening photochemistries, respectively.
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Affiliation(s)
- José P L Roque
- CQC-IMS, Department of Chemistry, University of Coimbra, Coimbra 3004-535, Portugal
| | - Mário T S Rosado
- CQC-IMS, Department of Chemistry, University of Coimbra, Coimbra 3004-535, Portugal
| | - Rui Fausto
- CQC-IMS, Department of Chemistry, University of Coimbra, Coimbra 3004-535, Portugal
| | - Igor Reva
- CQC-IMS, Department of Chemistry, University of Coimbra, Coimbra 3004-535, Portugal.,CIEPQPF, Department of Chemical Engineering, University of Coimbra, Coimbra 3030-790, Portugal
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Roque JPL, Nunes CM, Fausto R. Matrix Isolation in Heterocyclic Chemistry. HETEROCYCLES 2022. [DOI: 10.1002/9783527832002.ch12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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UV-induced -OCH 3 rotamerization in a matrix-isolated methoxy-substituted ortho-hydroxyaryl Schiff base. Photochem Photobiol Sci 2022; 21:835-847. [PMID: 35076900 DOI: 10.1007/s43630-021-00166-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Accepted: 12/27/2021] [Indexed: 10/19/2022]
Abstract
A new methoxy-substituted ortho-hydroxyaryl Schiff base, 4-(3-methoxy-2-hydroxybenzylidene-amino) phenol was synthesized from 4-aminophenol and 2-hydroxy-3-methoxybenzaldehyde in methanol solution and characterized by 1H-NMR, 13C-NMR and infrared spectroscopies and elemental analysis. The compound was isolated in a cryogenic (10 K) argon matrix, and the analysis of the infrared spectrum of the matrix-isolated compound revealed that it corresponds to the E-enol-imine isomeric form, with 3 different conformers being present in the matrix. These conformers share as common structural features the conformation of the free hydroxyl group (trans relatively to the para-substituent of the ring) and the presence of an OH…N intramolecular H-bond involving the methoxy-substituted phenol ring and the azomethine bridge, while they differ in the orientation of the methoxy-substituent group. The structures and relative energies of the conformers of the molecule, and relevant barriers for their interconversion were obtained through quantum chemical calculations, which were also used to calculate the infrared spectra of the different forms. Calculations were also carried out for the higher-energy Z-enol-imine and keto-amine forms of the compound. Upon UV (230 nm) irradiation, -OCH3 rotamerization was observed, leading to conversion of the lowest energy conformer, where the methoxy group is aligned with the plane of the ring, into the other two conformers initially present in the matrix, in which the OCH3 group is out-of-the-plane of the ring. As for other phenolic compounds previously studied, spontaneous quantum mechanical tunneling conversion of the cis-OH conformers present in the gas-phase into the three observed conformers was found to take place during matrix deposition.
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Lopes Jesus AJ, Rosado MTS, Fausto R, Reva I. UV-induced radical formation and isomerization of 4-methoxyindole and 5-methoxyindole. Phys Chem Chem Phys 2020; 22:22943-22955. [PMID: 33026378 DOI: 10.1039/d0cp04354k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Monomers of 4-methoxyindole and 5-methoxyindole trapped in low-temperature xenon matrices (15-16 K) were characterized by IR spectroscopy, in separate experiments. Each compound was shown to adopt the most stable 1H-tautomeric form. The photochemistry of the matrix-isolated compounds was then investigated by exciting the matrices with narrowband UV light with λ ≤ 305 nm. Two main photoproducts, similar for each compound, have been detected: (1) 4-methoxy- or 5-methoxy-indolyl radical, resulting from cleavage of the N-H bond; (2) 3H-tautomers (4-methoxy- or 5-methoxy-) with the released hydrogen atom reconnected at the C3 ring carbon atom. The presence of the two types of photoproducts in the UV-irradiated matrices was confirmed by comparison of their B3LYP/6-311++G(d,p) calculated IR spectra with the experimental spectra emerging upon the irradiations. The mechanism of the observed phototransformations was elucidated by Natural Bond Orbital and Natural Resonance Theory computations on the methoxy-substituted indolyl radicals resulting from the N-H bond cleavage. The highest natural atomic spin densities were predicted at the C3 and N1 positions of the indolyl ring, corresponding to a predominance of the resonance structures with the radical centres located at these two atoms. As a whole, the obtained experimental and theoretical data allowed establishing a general pattern for the photochemistry of methoxyindoles under matrix-isolation conditions.
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Affiliation(s)
- A J Lopes Jesus
- University of Coimbra, CQC, Department of Chemistry, 3004-535, Coimbra, Portugal.
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Reva I, Lapinski L, Lopes Jesus AJ, Nowak MJ. Photoinduced transformations of indole and 3-formylindole monomers isolated in low-temperature matrices. J Chem Phys 2017; 147:194304. [DOI: 10.1063/1.5003326] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Igor Reva
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Leszek Lapinski
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - A. J. Lopes Jesus
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
- CQC, Faculty of Pharmacy, University of Coimbra, 3004-295 Coimbra, Portugal
| | - Maciej J. Nowak
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
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Menzel JP, Noble BB, Lauer A, Coote ML, Blinco JP, Barner-Kowollik C. Wavelength Dependence of Light-Induced Cycloadditions. J Am Chem Soc 2017; 139:15812-15820. [DOI: 10.1021/jacs.7b08047] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Jan P. Menzel
- School
of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia
- Macromolecular
Architectures, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76131 Karlsruhe, Germany
| | - Benjamin B. Noble
- Australian
Research Council Centre of Excellence for Electromaterials Science,
Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - Andrea Lauer
- School
of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia
- Macromolecular
Architectures, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76131 Karlsruhe, Germany
- Institut
für Biologische Grenzflächen, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Michelle L. Coote
- Australian
Research Council Centre of Excellence for Electromaterials Science,
Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia
| | - James P. Blinco
- School
of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia
| | - Christopher Barner-Kowollik
- School
of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia
- Macromolecular
Architectures, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76131 Karlsruhe, Germany
- Institut
für Biologische Grenzflächen, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
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Nowak MJ, Reva I, Rostkowska H, Lapinski L. UV-induced hydrogen-atom transfer and hydrogen-atom detachment in monomeric 7-azaindole isolated in Ar and n-H2 matrices. Phys Chem Chem Phys 2017; 19:11447-11454. [DOI: 10.1039/c7cp01363a] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Upon UV excitation, the N1H form of 7-azaindole isolated in an Ar matrix transforms into N7H, C3H tautomers and the 7-azaindolyl radical; whereas only C3H and 7-azaindolyl radical products are photogenerated in solid H2 environment.
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Affiliation(s)
- Maciej J. Nowak
- Institute of Physics
- Polish Academy of Sciences
- 02-668 Warsaw
- Poland
| | - Igor Reva
- CQC
- Department of Chemistry
- University of Coimbra
- 3004-535 Coimbra
- Portugal
| | - Hanna Rostkowska
- Institute of Physics
- Polish Academy of Sciences
- 02-668 Warsaw
- Poland
| | - Leszek Lapinski
- Institute of Physics
- Polish Academy of Sciences
- 02-668 Warsaw
- Poland
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