Electrochemical and ESR studies of aromatic nitroso spin traps

Gronchi, G.; Tordo, Paul

doi:10.1163/156856793x00352

Cited by 20 publications

(14 citation statements)

References 10 publications

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“…The spectra exhibit large hyperfine splitting ( a iso ≈ 3.1 mT) between three equally intensive lines. Large a iso values can be attributed to nitroso radical cations (NO •+ ) rather than neutral nitroxyl ( > NO • ) radicals, which was also confirmed by DFT calculations, where an excellent agreement of calculated EPR parameters of the radical cations with experiment was found (see SI). Super-hyperfine splitting (SHFS) can be well recognized in the EPR spectrum of oxidized compound 5a .…”

Section: Resultssupporting

confidence: 67%

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

et al. 2016

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The effect of push-pull interactions in a series of variously substituted 5-nitrosopyrimidines on the strength of intramolecular hydrogen bonds, the height of rotational barriers around formally single bonds, UV-vis spectra and electrochemical behavior is explored. Intramolecular charge transfer (ICT) leads to a shift of electron density from electron-donating substituents, which is readily observable by NMR spectroscopy. The 5-nitroso group is able to form strong intramolecular hydrogen bonds with neighboring amino substituents. As a result, two rotamers with reversed orientation of the 5-nitroso group are observed for compounds with two different hydrogen-bond donors in neighboring positions. The barriers of interconversion between the two rotamers are strongly influenced by ICT, whereas the ratio of such rotamers depends primarily on the character of the hydrogen-bond donors. The ICT also significantly affects the position of UV-vis absorption maxima, which can be tuned in a broad range of 100 nm by the selection of appropriate substituents. Finally, ICT influences oxidation potential of the 5-nitrosopyrimidines and the stability of the resulting nitroso radical cations, the structures of which are determined by EPR spectroscopy.

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Section: Resultssupporting

confidence: 67%

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

et al. 2016

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“…Experiments that introduce the radical trap nitrosobenzene were run under a nitrogen atmosphere using distilled and degassed acetonitrile. Solutions were prepared with 5 mM 3 and 100 mM nitrosobenzene, to which the base was added to 20 mM.…”

Section: Methodsmentioning

confidence: 99%

Reactivity of [{Mn^IV(salpn)}₂(μ-O,μ-OCH₃)]⁺ and [{Mn^IV(salpn)}₂(μ-O,μ-OH)]⁺: Effects of Proton Lability and Hydrogen Bonding

et al. 1999

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It was previously shown that the addition of 1 equiv of a strong acid to [Mn(IV)(salpn)(&mgr;-O)](2), 1, generates the oxo/hydroxo complex [{Mn(IV)(salpn)}(2)(&mgr;-O,&mgr;-OH)](CF(3)SO(3)), 2, which emphasized the basicity of the &mgr;(2)-O(2)(-) units in the [Mn(IV)(&mgr;-O)](2) dimers. We now demonstrate the inherent nucleophilicity of those &mgr;(2)-O(2)(-) units by showing that the addition of methyl triflate to 1 results in formation of the oxo/methoxo-bridged Mn(IV) dimer [{Mn(IV)(salpn)}(2)(&mgr;-O,&mgr;-OCH(3))](CF(3)SO(3)), 3. EXAFS analysis of 3 demonstrates that alkylation of an oxo bridge results in the same structural modification of the [Mn(IV)(&mgr;-O)](2) core as an oxo bridge protonation. Electrochemical and spectroscopic comparisons of 3 to 2 indicate that 3 is a good electronic structure analogue for 2 without the complication of proton lability and hydrogen bonding. Indeed, 2 and 3 react nearly identically with hydrogen peroxide and with strong acids. In contrast, the products of their reactions with amines, acetate, and triphenylphosphine are dramatically different. The proton lability of 2 results in simple proton transfer, circumventing the slower redox reactions of these substrates with 3. Isotopic labeling, kinetic, and EPR-monitored radical trap studies lead to a proposed reduction-oxidation mechanistic scheme for the reactions of 3 with amines and triphenylphosphine. The Mn(III) product of this reaction, [Mn(III)(salpn)(Ph(3)PO)](CF(3)SO(3)), was isolated and crystallographically characterized as a dimerized complex. The redox nature of the reactions is confirmed by trapping of a reduced Mn intermediate which is identified by EPR spectroscopy. Comparison of the reactions of 2 and 3 demonstrates the dramatic effect of proton lability and hydrogen bonding on reactivity, and suggests how metalloenzymes may regulate active site reactivity to produce very different catalytic activities with similar active site structures. Furthermore, it also emphasizes that caution should be used when the reactivity of model compounds with easily and rapidly dissociable protons is assessed.

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“…The method has been applied to compounds of a wide range of structures, including aromatic amines, 18 phosphines, 79 diazoalkanes, 30 nitrosoarenes, 38 carotinoids, 80 azoalkanes, 81 cycloalkenes, 82 pagodanes, 83 and tetrathiofulvalenes. 42…”

Section: Anodic Oxidationmentioning

confidence: 99%

“…The technique can be applied to essentially any substrate with an ionisation energy below that of the Freon, which is ca. 11 eV, and it has been applied extensively to alkanes, 8 cycloalkanes, 86, 87 alkenes, 88 ethers, 13 alkyl halides, 14 carbonyl compounds, 89 nitroso compounds, 38 azo compounds, 90 imines, 91 arenes, 92 heteroaromatics, 93 organometallics, 94 and compounds of P, 95 S, 96 and Te. 97 The gamma ray interacts with the Freon give the Freon radical cation with the ejection of an electron.…”

Section: γ-Irradiation In Freonsmentioning

confidence: 99%

The Generation of Organic Radical Cations: A Guide to Current Practice for EPR Spectroscopic Studies

Davies

2001

Journal of Chemical Research

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Electrochemical and ESR studies of aromatic nitroso spin traps

Cited by 20 publications

References 10 publications

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

Reactivity of [{Mn^IV(salpn)}₂(μ-O,μ-OCH₃)]⁺ and [{Mn^IV(salpn)}₂(μ-O,μ-OH)]⁺: Effects of Proton Lability and Hydrogen Bonding

The Generation of Organic Radical Cations: A Guide to Current Practice for EPR Spectroscopic Studies

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Electrochemical and ESR studies of aromatic nitroso spin traps

Cited by 20 publications

References 10 publications

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

Tunable Push–Pull Interactions in 5-Nitrosopyrimidines

Reactivity of [{MnIV(salpn)}2(μ-O,μ-OCH3)]+ and [{MnIV(salpn)}2(μ-O,μ-OH)]+: Effects of Proton Lability and Hydrogen Bonding

The Generation of Organic Radical Cations: A Guide to Current Practice for EPR Spectroscopic Studies

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Reactivity of [{Mn^IV(salpn)}₂(μ-O,μ-OCH₃)]⁺ and [{Mn^IV(salpn)}₂(μ-O,μ-OH)]⁺: Effects of Proton Lability and Hydrogen Bonding