Radical Cation of Naphthalene on H−ZSM-5 Zeolite and in CFCl<sub>3</sub> Matrix. A Theoretical and Experimental EPR, ENDOR, and ESEEM Study

Erickson, Roland; Benetis, Nikolas P.; Lund, A.; Lindgren, Mikael

doi:10.1021/jp9631994

Cited by 30 publications

(35 citation statements)

References 32 publications

(61 reference statements)

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“…Characteristic g-value and the way of formation suggest that these centers should be attributed to aromatic p-radicals formed via secondary reactions of naphthalene cation-radicals that are supposed to be primary radical species formed upon adsorption of naphthalene onto the mordenites [30,31]. Despite rather mild conditions of naphthalene adsorption we were unable to find signals typical for naphthalene cationradicals on zeolites.…”

Section: Formation Of Radicals Upon Adsorption Of Naphthalenementioning

confidence: 89%

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

et al. 2006

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During the study of mordenite with the EPR technique, three EPR signals centered at g = 4.3; g = 2.4 and g = 1.98 were evidenced. The first two were attributed to Fe 3+ ions (signal at g = 4.3 typical to isolated framework iron species, signal at g = 2.4 characteristic to agglomerated non-framework ones). The signal at g = 1.98 was assigned to Cr 5+ ions. All these cations are present in the solid as impurities. Furthermore, under certain conditions the Cr 5+ ions can be in interaction with two equivalent 27 Al nuclei according to a formation of a superhyperfine structure in the EPR signals. After adsorption of naphtalene on the mordenite samples, organic p-radicals are formed via secondary reactions of primary cation-radicals nearby the aluminum atoms of the mordenite framework. The formation of radicals seems to be correlated to the presence of impurities in the solids. Thus not only acidity but also content of transition metals may be an important factor in the formation of radicals.

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Section: Formation Of Radicals Upon Adsorption Of Naphthalenementioning

confidence: 89%

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

et al. 2006

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“…In this case it may be possible to observe all the principal components of, e.g., a hfc tensor in the same spectrum. This is demonstrated by simulations of experimental spectra made of both the biphenyl [162] and the naphthalene radical cations [163].…”

Section: Simulation Of Endor Powder Spectramentioning

confidence: 90%

“…The orientational variations of the transition probabilities were significant enough to require that an average is taken in a powder. The relative differences, ( W [162] and naphthalene on H-ZSM-5 zeolite [163]. In these cases the hfc anisotropy is of the same order as the isotropic contribution.…”

Section: Applications Of First Order Endor Theorymentioning

confidence: 90%

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Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Erickson

Lund

2014

Applications of EPR in Radiation Research

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Applications of EPR and ENDOR simulations of relevance in radiation research involving free radicals, radical pairs, triplet states and to less extent metal complexes are treated. Early fundamental work involving in situ radiolysis of liquids and stickplot analysis of spectra is reviewed, while single crystal analysis is only briefly discussed. The analysis of data obtained with continuous wave methods of species trapped in disordered solids, "powders" is emphasized. Simulations based on first and second order and exact theory are described and exemplified. Methods to obtain parameters for the dynamics of radicals in irradiated solids and for the simulation of spectra at microwave saturation are discussed. Procedures for the simulation of powder ENDOR spectra of radicals are described in detail, with special emphasis on the influence of nuclear quadrupole couplings due to nuclei with I ≥ 1. EPR and ENDOR simulation programs known to us are presented in an Appendix, including addresses for downloading when available.

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“…The naphthalene radical cation generated by UV-or X-irradiation on HZSMS zeolite and in frozen CFC13 is investigated by EPR, ENDOR and ESEEM spectroscopic methods [175]. Analysis of powder EPR line shape was made possible by the simultaneous use of ENDOR and ESEEM spectroscopies.…”

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confidence: 99%

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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Radical Cation of Naphthalene on H−ZSM-5 Zeolite and in CFCl₃ Matrix. A Theoretical and Experimental EPR, ENDOR, and ESEEM Study

Cited by 30 publications

References 32 publications

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Electron‐transfer Reactions of Aromatic Compounds

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Radical Cation of Naphthalene on H−ZSM-5 Zeolite and in CFCl3 Matrix. A Theoretical and Experimental EPR, ENDOR, and ESEEM Study

Cited by 30 publications

References 32 publications

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

EPR investigation, before and after adsorption of naphtalene, of mordenite containing Fe3+ and Cr5+ ions as impurities

Applications of EPR and ENDOR Spectrum Simulations in Radiation Research

Electron‐transfer Reactions of Aromatic Compounds

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Radical Cation of Naphthalene on H−ZSM-5 Zeolite and in CFCl₃ Matrix. A Theoretical and Experimental EPR, ENDOR, and ESEEM Study