Free radicals, ESR

Spin-density distributions are inherent features of free radicals. Esr experiments take place when the radical is in its electronic ground state and the measurement of the spin distribution constitutes only a minute perturbation of the system. This feature and the fact that esr hyperfine splitting can be measured with high precision makes the esr method ideally suited for the study of substituent effects. Therefore, if spin delocalization is accepted as a measure of stabilization, the data in Table 6 provide quantitative information. However, these are percentage values and not energies of stabiliza-... 

Alkyl Free Radicals. The primary alkyl free radical, RCH./, has been postulated to exist in gamma-irradiated polyethylene (23), but its presence has never been unambiguously demonstrated. If all the a and p protons interacted equally with the unpaired electron, the primary alkyl free radical ESR spectrum should consist of five lines, in contrast to those of the secondary and tertiary alkyl radicals whose ESR spectra should consist of six and eight lines, respectively (the latter calculated for the tertiary free radical in polypropylene). The existence of the secondary... 

JCO38 - Ei -1.27 SSCE - sttd 1. free radical,ESR C,p AL98... 

Berdnikov, B. M., Doctorov, A.B., and Makarshin, L.L. (1980) Dipole-dipole broadening of free radicals ESR spectra in the presence of paramagnetic ions, Theoretical and Experimental Chemistry (Kiev) 16, 765-771. 

Electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy has developed at an outstanding pace since its discovery in 1945 (Zavoiskii 1945), so that at present the technique is very well understood in its many aspects. In wood chemistry, ESR has become an essential tool for the study of the structure and dynamics of molecular systems containing one or more unpaired electrons, i.e., free radicals. ESR has found applications as a highly sensitive tool for the detection and identification of free radical species in lignin and lignin model compounds (Steelink 1966, Kringstad and Lin 1970). A recent literature review of free radicals in wood chemistry is available (Simkovic 1986). 

Mitochondrial membrane preparations contain free radical ESR signals (Fig. 9) that have been attributed [151-153] to various forms of ubisemiquinones located in... 

The spectral analysis of paramagnetic species featuring hyperfine structure is emphasized in textbooks [1 ] since it helps identify the chemical and electronic structure of the species under study. A majority of the studies has involved free radicals. ESR analysis of hyperfine structure is discussed in Sections 3.2.2-3.2.6. ENDOR spectra of liquid samples are usually analysed visually, see Chapter 2 for examples, and [2] for a detailed account, including a description of a simulation program referenced in Section 3.2.7. 

It is the only direct method available to measure free radicals. ESR is used to study both the radicals and the reactions, chemical and physical, which create or modify free radicals. Examples of reactions that can create or change free radicals are electrochanical reactions, exposure to UV radiation, and exposure to ionizing radiation, among others. ESR samples can be liquid, such as oil, blood, or saliva, solid, or gaseous, such as measurement of soot particulates in air. ESR is both a qualitative and quantitative technique, measuring the type and concentration of free radicals in a sample. Qualitative information is obtained from the g value of a peak, while quantitative results are obtained by integrating the area under the peaks. 

Free-radical immunoassay Free radicals ESR Complex labelling complex instrumentation (34)... 

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