Electron spin resonance radical investigations

This different behavior can be explained by the conformation of the radicals and by stereoelectronic effects [6]. Electron spin resonance (ESR) investigations have revealed that the D-glucopyranosyl radical 7 does not adopt the 4C1 conformation 7a, but is distorted into the B2 5 shape 7b (Scheme 5) [7,8], The equatorial-like attack at the boat conformer... 

H.-G. Korth, R. Sustmann, J. Dupuis, and B. Giese, Electron spin resonance spectroscopic investigation of carbohydrate radicals. Part 2. Conformation and configuration in pyranos-l-yl radicals, J. Chem. Soc. Perkin Trans. 2 1453 (1986). 

Korth H, Sustmann R, Groninger KS, Witzel T, Giese B (1986) Electron spin resonance spectroscopic investigation of carbohydrate radicals. Part 3. Conformation in deoxypyranosan-2-, 3-, and 4-yl radicals. J Chem Soc Perkin Trans 2 1461-1464... 

Several electron spin resonance (ESR) investigations have established that free radicals are formed as a result of interatomic bond scission under mechanical stress and during fracture of polymers The application of ESR spectroscopy,... 

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

Investigations on the electron spin resonance of the radical anions 29 31> of [2.2]-and higher [n.n]paracyclophanes have shown that delocalization of the unpaired electrons over both aromatic nuclei is scarcely possible until the number of bridge members n >3 31>. In open-chain compounds of the type Ar-[CH2] -Ar the corresponding condition is n> 1. This would suggest that the mechanism responsible for the transfer of elec-... 

Endo et al. investigated the reductive decomposition of various electrolytes on graphite anode materials by electron spin resonance (ESR). In all of the electrolyte compositions investigated, which included LiC104, LiBF4, and LiPFe as salts and PC, DMC, and other esters or ethers as solvents, the solvent-related radical species, which were considered to be the intermediates of reductive decomposition, were detected only after prolonged cathodic electrolysis. With the aid of molecular orbital calculation, they found that the reduction of salt anion species is very difficult, as indicated by their positive reduction enthalpy and that of free solvent (A/4 — 1 kcal mol ). However, the coordination of lithium ions with these solvents dramatically reduces the corresponding reduction enthalpy (A/ —10 kcal mol ) and renders the reaction thermodynamically favored. In other words, if no kinetic factors were to be considered, the SEI formed on carbonaceous anodes... 

P. Hofer, A. Grupp, H. Nebenfiihr, and M. Mehring, Hyperfine sublevel correlation (HYSCORE) spectroscopy—A 2D electron spin resonance investigation of the squaric acid radical, Chem. Phys. Lett., 132 (1986) 279-282. 

The electron spin resonance (ESR) spectra of the radical anion of 2,2 -bipyridine, sometimes in the form of its alkali metal com-plgx, 71.175,177.299-304 radical anion of 3,3 -bipyridine, ° and the radical anion of 4,4 -bipyridine, ° ° usually obtained by reduction of the bipyridines with an alkali metal, have been measured, and hyperfine splitting constants were assigned. Related biradical species have also been investigated. The ESR spectrum of the 4,4 -bipyridinium radical cation, of which... 

Diradical species 35a and 35b, in which two imino nitroxide 35a or nitronyl nitroxide 35b radical centers are attached to thieno[2,3-. ]thiophene, were prepared and their intramolecular exchange interactions were investigated in frozen solutions by means of electron spin resonance (ESR) spectroscopy and magnetic susceptibility measurements at cryogenic temperature <1996T6893>. 

ESR Spectroscopy. Electron Spin Resonance spectroscopy is an important technique for investigating the role of radical intermediates in radiation chemistry. The technique has been used widely for many years in the study of radicals occurring in irradiated solid polymers (.6,7). However, by their very nature, such species are reactive and may only exist in low concentration. The identification of these species can also be a problem since in the majority of polymers the environment of the radicals leads to broad, unresolved ESR spectra, which makes detailed spectral analysis difficult. In recent years, many of these problems of sensitivity and resolution have been reduced by more sensitive and stable ESR spectrometers and by development of new methods of data handling and manipulation. 

Since the heroic early mechanistic investigations, there have been two developments of major significance in radical chemistry. The first was the advent of electron spin resonance (ESR) spectroscopy (and the associated technique of chemically induced dynamic nuclear polarisation, CIDNP) [24], which provided structural as well as kinetic information the second is the more recent development of a wide range of synthetically useful radical reactions [20]. Another recent development, the combination of the pulse radiolysis and laser-flash photolysis techniques, is enormously powerful for the study of radicals but beyond the scope of this book. 

The structures of compounds containing a 1,3,2-dithiazole ring (1,3,2-dithiazolidines, 1,3,2-dithiazoles, 1,3,2-dithia-zolium cations and radicals) were extensively investigated by X-ray and electron diffraction between 1980 and 1990 <1996CHEC-II(4)433>. Nuclear magnetic resonance (NMR) spectroscopy was found to be very effective for elucidation of the structure of 1,3,2-dioxazoles and 1,3,2-dithiazoles. Electron spin resonance (ESR) spectra of the 1,3,2-dithiazolyl radicals gave important information on their structures. 

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