Electron paramagnetic resonance spectra of phenyl radicals

Tolkachev, V. A.; Chkheidze, I.I.; Buben, N.Ya.

doi:10.1007/bf00744132

Cited by 11 publications

(6 citation statements)

References 4 publications

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“…The hyperfine structure of the spectrum shows two hydrogen couplings at 16 G and two smaller couplings at 6 G with a g value of 2.0025. These parameters are those expected for the phenyl radical in a glassy matrix. , Clearly, electron attachment results in a cleavage of the carbon halogen bond releasing the phenyl radical as shown in the reaction below: We find that detectable amounts of phenyl radicals are also generated from Ph 2 I + in aqueous ethylene glycol glass . However, the phenyl radicals trapped in ethylene glycol decay on standing at 77 K likely through hydrogen abstraction from the matrix.…”

Section: Resultssupporting

confidence: 66%

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Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?

1999

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One-electron reduction of o,o‘-diphenylenebromonium (DPB) and o,o‘-diphenyleneiodonium (DPI) cations in low-temperature glasses produces free radical intermediates whose halogen hyperfine couplings suggest significant spin densities on bromine (0.13) and iodine (0.30). An adequate theoretical description of these species has been obtained at both semiempirical (PM3) and density functional levels of theory. These calculations show these species are a planar conformation of the 2-halobiphenyl-2‘-yl radicals, stabilized through intramolecular three-electron (or σ*) carbon−halogen bonding. Theory also predicts a nonequivalence of the C−X bonds and unsymmetrical spin density distribution over the two C−X bonding carbons. As compared to DPB, the DPI radical gives evidence for more equivalent bonding of the iodine to both carbons, accompanied by lower potential barriers for intramolecular iodine atom migration (1−2 kcal mol-1) along the σ*-bond. In the case of 3-nitrosubstituted DPI (NDPI) the one-electron-reduced intermediate was observed both as a σ*-radical (in polar glasses) and as a π*-radical (when intercalated into DNA). Calculations suggest that the change from σ* to π* on intercalation into DNA is driven both by electric field of the DNA backbone and by π-stacking of NDPI with DNA bases. One-electron-reduced diphenylenehalonium derivatives were not found to undergo intramolecular free radical addition leading to a cyclohexadienyl-type adduct. This result is supported by theoretical calculations indicating that such a process would be endothermic by 13.9 kcal mol-1 at the ROMP2/6-31G* level.

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Section: Resultssupporting

confidence: 66%

“…These parameters are those expected for the phenyl radical in a glassy matrix. 18,19 Clearly, electron attachment results in a cleavage of the carbon halogen bond releasing the phenyl radical as shown in the reaction below:…”

Section: Primary Reduction Intermediates (A) Diphenyliodoniummentioning

confidence: 99%

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?

1999

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“…The intensity of these spectra depended upon pH, flow rate, and reactant concentration becoming more intense at higher pH, lower flow rate, and lower concentration. Hydroxycyclohexadienyl radicals were identified by the ~30-G proton splitting by the CHOH ring proton and the parameters were checked against results of studies specifically of this type of radical.17,18 These radicals can be formed at pH >10 as a result of the conversion of SO4•-to OH by SO4-+ OH" -»0H + S042" (2) with a rate constant of 6.5 X 107 M-1 sec-1. 19 At lower pH values (7-9), this reaction cannot be significant and some other mechanism must exist for producing hydroxycyclohexadienyl radicals.…”

Section: Resultsmentioning

confidence: 99%

Electron spin resonance studies of phenyl and pyridyl radicals in aqueous solution

Zemel¹,

Fessenden²

1975

J. Phys. Chem.

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Publication costs assisted by Carnegie-Meilon University and the U. S. Energy Research and Development AdministrationESR spectra of a number of phenyl and 2-pyridyl radicals have been detected in aqueous solution. Two methods of radical production were used, namely, reaction of SO4.-produced by photolysis of &Os2-with aromatic carboxylate ions and reaction of eaq-produced by radiolysis with aromatic bromides. Most radicals had only carboxyl groups as further substituents. The proton hyperfine constants of the phenyl radicals, a, -17, um -6, and up -2 G, are readily assigned on the basis of effects of the various substitutions and agree well with previous determinations for radicals in the solid state. With four phenyl radicals containing two to four carboxyl groups it was also possible to detect all of the possible 13C containing isomers at natural abundance. A hyperfine constant of -135 G for the carbon at the radical site confirms the u nature of phenyl radical. The other ring 13C hyperfine constants are uoc -7.5, urnc -13, and upc -1.5 G.Both 14N and proton hyperfine constants were determined for the 2-pyridyl radicals. Only the 14N value (-27 G) was known previously. The g factors of phenyl and 2-pyridyl radicals are low (near or below the free electron value) reflecting their u nature. The presence of carboxyl groups in a phenyl radical affects the g factor in an additive fashion with increments of 13, -2, and -3 units in the fifth decimal place for ortho, meta, and para substituents, respectively. The observation of phenyl and 2-pyridyl radicals demonstrates in a direct way that these radicals are formed in the two above-mentioned reactions. (One example each of a 4-pyridyl and a pyrazyl radical were also produced and studied.) Phenyl and 2-pyridyl radicals with no ortho carboxyl group were found to be very reactive toward addition to another aromatic molecule and were best detected using low concentrations (5 X lov4 M ) of aromatic bromide. Spectra of the unsubstituted phenyl and 2-pyridyl radicals were obtained in this way from the corresponding bromides. At higher solute concentrations such as used for the decarboxylation reactions these radicals react further to form adducts of the cyclohexadienyl type. Radicals with an ortho carboxyl group (for example, 2-carboxylphenyl radical produced from phthalate) are much less reactive toward addition and could be studied at higher concentrations of the starting compound. Reaction of SO4--with acids in which three (or more) adjacent carboxyl groups are present leads preferentially to loss of a central or interior carboxyl group. To provide data for comparison with earlier indirect studies, a number of adducts of phenyl and pyridyl radicals to CH2=N02-and trimesate were studied and their hyperfine constants determined. In the latter cases it was found that the ortho and meta protons in the phenyl radical which has added (i.e., the side group in the final cyclohexadienyl radical) can produce splittings of -0.05 and -0.3 G, respectively. The radicals detected in exp...

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“…When excess of benzyl bromide and HMPA (1:1) is condensed on the compact copper film (the thickness of the film is about 10 −4 mm), losses of UHF power in the sample increase due to an increase in the electric conductivity, which results in consider- 16.5 ± 1 5.5 ± 0.5 -5.5 ± 0.5 [35] able worsening of the resolution of the ESR spectra. Paramagnetic species that appeared in the benzyl bromide-HMPA atomic copper systems do not differ from those formed when the compact copper film is formed.…”

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confidence: 98%

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

Егоров¹,

Matyukhova²,

Анисимов³

2005

Int J of Chemical Kinetics

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The reaction of copper with benzyl bromides in hexamethylphosphoramide has been studied. The kinetic and thermodynamic parameters of the reaction have been obtained. Hammett plots of log (k/k o ) vs the substituent constant σ gave good correlations (ρ = 0.15, S ρ = 0.02, r = 0.954). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. In the absence of atmospheric oxygen, the oxidative dissolution of copper occurred by the mechanism of single-electron transfer with the formation of 1,2-diphenylethane and copper(I) complexes. The stereochemistry and intermediates compound was also investigated.The reaction mechanism is discussed. C 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: [296][297][298][299][300][301][302][303][304][305] 2005

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Electron paramagnetic resonance spectra of phenyl radicals

Cited by 11 publications

References 4 publications

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?

Electron spin resonance studies of phenyl and pyridyl radicals in aqueous solution

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

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Electron paramagnetic resonance spectra of phenyl radicals

Cited by 11 publications

References 4 publications

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar2I• or Simply a New σ*-Radical?

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar2I• or Simply a New σ*-Radical?

Electron spin resonance studies of phenyl and pyridyl radicals in aqueous solution

Kinetics and mechanism of the reaction of benzyl bromide with copper in hexamethylphosphoramide

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Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?

Electron Spin Resonance and Molecular Oribtal Study of One-Electron-Reduced O,O‘-Diphenylenehalonium Cations: First Evidence for a Diaryliodine Radical, Ar₂I^• or Simply a New σ*-Radical?