15N-CIDNP during Photonitration of Phenol with Tetranitromethane and Reactions with Nitric and Nitrous Acid

Lehnig, M.; Schürmann, Klaus

doi:10.1002/(sici)1099-0690(199805)1998:5<913::aid-ejoc913>3.0.co;2-r

Cited by 9 publications

(6 citation statements)

References 34 publications

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“…All 15N NMR experiments were performed with a Bruker DPX 300 spectrometer with a modified 10 mm probe head [5]. The probe head is equipped with a light conductor which was connected to a LEXEL 95 argon ion laser (Polytec Inc.).…”

Section: Methodsmentioning

confidence: 99%

“…The nitration mechanism is similar to those with nitric acid, nitrous acid or peroxynitrite as nitrating agents [5][6][7].…”

Section: Introductionmentioning

confidence: 93%

“…During irradiation of 1 whithin the probe head of a 15 N NMR spectrometer, the 15N NMR signals of the nitration products 2 and 3 appear in emission, for further details see [5] and Table 1. The magnitude of the 15N CIDNP effects is comparable to those observed during the nitration of 1 with nitric acid, nitrous acid and peroxynitrite indicating that the radical reaction is the main, if not the only reaction.…”

Section: Photochemical Nitration Of Phenol and 35-dimethylphenol Witmentioning

confidence: 99%

“…2,6-Dimethyl-p-benzoquinone (7) is formed in a 12% yield as a side product of the reaction which is identified after workup of the reaction mixture with column chromatography. The nature of the photochemical nitration reaction as well as the product ratio are identical to those of 1 [5]. The ' 5 N CIDNP effects are built up in radical pairs which are formed by T states of the triad or independently generated radical cations 4+' or 3,5-dimethylphenoxyl radicals and 'NO 2 , see Eq.…”

Section: Photochemical Nitration Of Phenol and 35-dimethylphenol Witmentioning

confidence: 99%

“…If TNM is irradiated with phenol (1) in the probe head of a ' SN nuclear magnetic resonance (NMR) spectrometer, the ' sN NMR signals of the nitration products 2-nitrophenol (2) and 4-nitrophenol (3) appear in emission indicating the formation of 2 and 3 via collapse of the triad from triplet (T) states or by recombination of free diffusing (F) radicals 1 +' or PhO and 'NO2, ArH = 1, see Table 1) [5]:…”

Section: Introductionmentioning

confidence: 99%

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Mechanistic studies of the photochemical nitration of phenols, 1,2-dimethoxybenzene and anisoles with tetranitromethane by15N CIDNP

Schürmann

Lehnig

2000

Appl. Magn. Reson.

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During the photochemical nitration of phenol, 3,5-dimethylphenol and 1,2-dimethoxybenzene (8) with ' 5 N-enriched tetranitromethane, the ' 5 N nuclear magnetic resonance (NMR) signals of the nitro products 2-nitrophenol, 4-nitrophenol, 2-nitro-3,5-dimethylphenol, 4-nitro-3,5-dimethylphenol and 1,2-dimethoxy-4-nitrobenzene (9) appear in emission. The nuclear polarizations are built up in radical pairs formed by radical cations or in case of the phenols by phenoxyl radicals and 'NO 2 . They are generated by photoreactions from excited triplet states of the reactants or by free radical encounters. With 8, I,2-dimethoxy-4-trinitromethylbenzene is also formed which slowly converts to 9. In contrast to this, the ' sN NMR signals of the nitration products of anisole (11) and 3,5-dimethylanisole (12), 2-nitroanisole, 4-nitroanisole, 3,5-dimethyl-2-nitroanisole and 3,5-dimethyl-4-nitroanisole appear in enhanced absorption indicating the appearance of singlet radical pairs [11 , 'NO 2 1s and [12,'NO2] s in which the nuclear polarizations are built up. The singlet radical pairs are formed by decomposition of an unstable intermediate, most probably a nitro-trinitromethyl adduct.

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Section: Methodsmentioning

confidence: 99%

“…The nitration mechanism is similar to those with nitric acid, nitrous acid or peroxynitrite as nitrating agents [5][6][7].…”

Section: Introductionmentioning

confidence: 93%

Section: Photochemical Nitration Of Phenol and 35-dimethylphenol Witmentioning

confidence: 99%

Section: Photochemical Nitration Of Phenol and 35-dimethylphenol Witmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Mechanistic studies of the photochemical nitration of phenols, 1,2-dimethoxybenzene and anisoles with tetranitromethane by15N CIDNP

Schürmann

Lehnig

2000

Appl. Magn. Reson.

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Photochemically Induced Dynamic Nuclear Polarization: Basic Principles and Applications

Cavagnero

2017

eMagRes

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Electron‐transfer Reactions of Aromatic Compounds

Gescheidt¹,

Khan²

2001

Electron Transfer in Chemistry

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Aromatic molecules are inclined to undergo electron-transfer reactions. The additional charges introduced by the electron-transfer process are efficiently stabilized by delocalization. Nevertheless rearrangements of the molecular skeleton or followup reactions can occur. The course of the electron-transfer reactions and the properties of the species thus formed are the subject of this section.In particular, we concentrate on the species formed after an one-electron transfer reaction. Starting from closed-shell diamagnetic precursors, paramagnetic stages, i.e. radical cations or radical anions are formed in this first step. To understand the properties and reactivity of these species, detailed knowledge in terms of charge and spin delocalization and electronic structure is an important prerequisite. This information is preferably derived from electronic and paramagnetic resonance (EPR and electron-nuclear multiple resonance-techniques such as ENDOR or Triple spectroscopy). It has recently been shown that the experimental results can be substantiated by the use of quantum-chemical calculations. In addition to Hartree-Fock-based ab initio procedures, calculations on the density-functional level of theory have been established as rather efficient tools. Therefore, before representing examples of electron-transfer-generated radicals a short survey of the computational methods is given.Another substantial factor directing the kinetic and thermodynamic stability of charged radicals is ion pairing. This phenomenon, although well established for many years, is often not directly distinct in experiments. To establish the importance of ion pairing, or, in other words, supramolecular interactions, a separate introductory chapter is dedicated to these aspects.The references are selected particularly from recent publications, without, however, ignoring some 'classical' contributions. In some sections topics are included which do not strictly represent aromatic molecules but involve interactions of ztype orbitals.

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15N-CIDNP during Photonitration of Phenol with Tetranitromethane and Reactions with Nitric and Nitrous Acid

Cited by 9 publications

References 34 publications

Mechanistic studies of the photochemical nitration of phenols, 1,2-dimethoxybenzene and anisoles with tetranitromethane by15N CIDNP

Mechanistic studies of the photochemical nitration of phenols, 1,2-dimethoxybenzene and anisoles with tetranitromethane by15N CIDNP

Photochemically Induced Dynamic Nuclear Polarization: Basic Principles and Applications

Electron‐transfer Reactions of Aromatic Compounds

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