Electron spin resonance silent

In the majority of cases, NMR spectroscopy has been used as a invaluable tool for structural elucidation for example, in the synthesis of 7, H and NMR spectra were in accordance with the desired structure, which was confirmed by X-ray crystallography <2004JA5493>. Also, in the structural elucidation of 3, sharp line H and NMR spectra were observed but the compound was ESR silent, therefore indicating a closed-shell species (ESR = electron spin resonance). 

The design temperature of 600°C. was chosen by considering coal as a free radical source. Electron spin resonance studies of coals (I) indicate that a rather sharp maximum in nonspin-paired electron content occurs in coals when processed in this temperature zone—i.e., 500°-550°C. Chlorine moreover can be converted to atomic chlorine by several energy sources—corona discharge, silent electric discharge, ca. 4700 A. light, etc. 

Electron paramagnetic resonance (EPR) spectroscopy (also called electron spin resonance (ESR) spectroscopy), is used to study paramagnetic species with one or more unpaired electrons, e.g. free radicals, diradicals, metal complexes containing paramagnetic metal centres, defects in semiconductors and irradiation effects in solids. While diamagnetic materials are EPR silent, paramagnetic species always exhibit an EPR spectrum. This consists of one or more lines, depending on the interactions between the unpaired electron (which acts as a probe ) and the molecular framework in which it is located. Analysis of the shape of the EPR spectrum (the number and positions of EPR lines, their intensities and line widths) provides information... 

Electron paramagnetic resonance spectroscopy has proved a valuable tool in the study of AdoCbl-dependent enzymes. AdoCbl itself is EPR-silent, but upon homolysis to form Cbl(II), two spins are formed, one on the cobalt (which now has low-spin d configuration) and one on the organic radical. Typically, the two unpaired electrons remain close enough in the enzymeis active site that they interact with one another to give complex, but informative, EPR spectra. 

In contrast with NMR spectroscopy, EPR spectroscopy is limited to systems in which there is an unpaired electron such as organic radicals or transition metals. Otherwise, the technique is spectroscopically silent. Typically in an NMR experiment, magnetic field is kept constant and frequency is varied. In EPR spectroscopy, frequency is kept constant and field is varied instead. Consequently, differences in spin state energies and hence resonance condition due to electron position and environment cannot be diagnosed by NMR style chemical shift since this is a frequency-based concept. Instead, an alternative concept needs to be originated, which is the concept of the g-value. 

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