Hyperfine anisotropy and mobility of organic radical cations in zeolites

Roduner, Emil; Crockett, Rowena; Wu, Longmin

doi:10.1039/ft9938902101

Cited by 35 publications

(36 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The available ESR experimental data of alkene cation radical in the chemical literature have been generated by three major techniques: namely, oxidation methods in liquid solutions, 9,15 chemisorption with solid state defects (or modified Lewis acid sites) on pretreated H-zeolites, 7,11 and photolysis or radiolysis of alkenes in various solid matrix isolation techniques at low temperatures. 8,10,[16][17][18][19][20][21][22][23][24][25][26] Some of the radiolysis ESR work have not been resolved and their assignments of the alkene cation radical conformations are ambiguous be-cause chemical active alkene cation radicals may have different chemical pathways even in the rigid zeolitic matrix as observed by this author and his co-workers. 7,11 The steady flow mixed system in combination with transitional metal ion oxidation in liquid solutions gives well-resolved ESR spectra of alkene cation radicals, 9 and aromatic radical cation dimer with intermolecular Jahn-Teller effect, 15 but they are limited to room temperature ranges experimentally.…”

Section: Resultsmentioning

confidence: 99%

“…The molecular and electronic structures of alkene radical cations have been widely investigated both in experimental studies [16][17][18][19][20][21][22][23][24][25][26][27][28] and theoretical calculations based on various molecular orbital calculations. [29][30][31][32][33][34][35][36][37][38][39][40] Much effort has been devoted to clarifying whether olefin radical cations are planar or twisted about the olefinic C-C central bond.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Shih

2003

J Chinese Chemical Soc

View full text Add to dashboard Cite

A large class of stereochemcial and related interactions in organic chemistry are repulsive and others are attractive, but the relative orientation of two methyl groups and the amount of energy required to twist one relative to the other (the hindered rotation energy barriers), or the alignment of such a group with respect to a conjugated ring to which it is attached (widely attributed to a mechanism called "hyperconjugation") are estimated to be small in compared with the total energy of the molecule.We used theories of both isotropic and anisotropic proton hyperfine interactions in the p-electron systems developed in the early sixties. They are approximated by the magnetic dipole nteractions between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals center on carbon atoms. We have extended these theories to the non-planar olefinic cation radicals, which are very important in biochemistry as well as in petroleum catalysis. A three dimensional electron spin density equation has been developed in this paper to handle some Jahn-Teller vibronic molecules. The new electron spin density equation related the observed proton hyperfine splittings to the non-planar structures of the open-chain alkene cation radicals generated by radiolysis and various chemical oxidation methods. The spin densities and the conformational calculations based on valence bond theory and symmetry principles are compared with some more elaborated molecular orbital calculations in the literature. The localized valence bond approaches are better in accord with our experimental results. The anomalous line-width effect of the four methyl groups observed in the 2,3-dimethyl-2-butene cation radicals also confirmed the positive sign of the electron-proton hyperfine constant of hyper-conjugation mechanism.A methyl substituent attached to a conjugated molecule often behaves as if it formed part of the region of conjugation; the charge appears to flow from the methyl group into the p electron system and it may also give rise to an appreciable dipole moment. Methylation also gives rise to an appreciable dipole moment, and the resultant red shift of electronic absorption bands is of some importance in the design of dye molecules.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Shih

2003

J Chinese Chemical Soc

View full text Add to dashboard Cite

show abstract

“…Roduner et al 46 , recorded anisotropic ESR spectra at ambient temperature from the radical cations of tetramethylethylene (TME) in H-ZSM-5 and of 2,5-dimethylhexa-2,4-diene (DMHD) in H-mordenite: the anisotropy becomes more pronounced as the temperature is lowered. From detailed simulations of the spectral parameters, these workers concluded that TME +• in H-ZSM-5 rotates about the plane of the molecule, as located at the channel intersections of this zeolite; it is proposed that HMHD +• undergoes a librational ("rattling") motion in the channels of H-mordenite, rather than a rotation about its long-axis.…”

Section: Dynamic Studiesmentioning

confidence: 99%

Unpaired Electrons as Probes of Catalytic Systems

Rhodes¹

2014

Science Progress

View full text Add to dashboard Cite

An overview is provided of the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review aims to demonstrate the considerable extent of scientific progress that has been made in this broad topic during the past few decades. Studies of catalytically active surfaces, including zeolites, are surveyed, and the detection of radical species, formed as intermediates in their reactions, using matrix isolation and spintrapping techniques. Radical cation formation in zeolites is discussed, and the employment of muon spin rotation and relaxation techniques to study the mobility of labelled radicals in various porous and catalytic media. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, degradation of environmental pollutants, hydrocarbon conversions, fuel cells and sensor devices employing graphene. The review concludes with recent developments in the study of enzymes and their reactions, using ESR-based methods.

show abstract

“…By means of temperature‐dependent EPR spectroscopy, Biglino et al found a translation movement or a rotary diffusion for NO 2 on mordenite, ferrierite, and ZSM‐5, Beta, L, X, and Y zeolites, dependent upon the respective structure 187. Roduner et al investigated the mobility of organic radical cations in zeolites by a quantitative analysis of the anisotropy of the hf splitting and the g tensors 188. They established that the radical cation formed through spontaneous oxidation of 2,3‐dimethylbut‐2‐ene in H‐ZSM‐5 zeolite at room temperature rotates about an axis vertically to the molecular plane, whereas the radical cation of 2,5‐dimethylhexa‐1,5‐diene in H‐mordenite undergoes rotational movement in the time scale of about 50 ns.…”

Section: Epr Spectroscopymentioning

confidence: 99%

In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis

Hunger

Weitkamp

2001

Angewandte Chemie Intl Edit

244

108

View full text Add to dashboard Cite

The development of new solid catalysts for use in industrial chemistry has hitherto been based to a large extent upon the empirical testing of a wide range of different materials. In only a few exceptional cases has success been achieved in understanding the overall, usually very complex mechanism of the chemical reaction through the elucidation of individual intermediate aspects of a heterogeneously catalyzed reaction. With the modern approach of combinatorial catalysis it is now possible to prepare and test much more rapidly a wide range of different materials within a short time and thus find suitable catalysts or optimize their chemical composition. Our understanding of the mechanisms of reactions catalyzed by these materials must be developed, however, by spectroscopic investigations on working catalysts under conditions that are as close as possible to practice (temperature, partial pressures of the reactants, space velocity). This demands the development and the application of new techniques of in situ spectroscopy. This review will show how this objective is being achieved. By the term in situ (Lat.: in the original position) is meant the investigation of the chemical reactions which are taking place as well as the changes in the working catalysts directly in the spectrometer.

show abstract

Hyperfine anisotropy and mobility of organic radical cations in zeolites

Cited by 35 publications

References 26 publications

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

A Generalized Unpaired Electron Spin Density Equation and Organic Hyperconjugation Mechanism

Unpaired Electrons as Probes of Catalytic Systems

In situ IR, NMR, EPR, and UV/Vis Spectroscopy: Tools for New Insight into the Mechanisms of Heterogeneous Catalysis

Contact Info

Product

Resources

About