Electron spin resonance radical compounds, identification

Inoue, K., Murayama, S., Seshimo, F., Takeba, K., Yoshimura, Y., and Nakazawa, H. (2005). Identification of phenolic compound in manuka honey as specific superoxide anion radical scavenger using electron spin resonance (ESR) and liquid chromatography with coulometric array detection. /. Sci. Food Agric. 85, 872-878. 

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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). 

Electron spin resonance (ESR, also known as electron paramagnetic resonance, EPR) is used for the detection and identification of electrogenerated products or intermediates that contain an odd number of electrons that is, radicals, radical ions, and certain transition metal species. Because ESR spectroscopy is a very sensitive technique, allowing detection of radical ions at about the 10 M level under favorable circumstances, and because it produces information-rich, distinctive, and easily interpretable spectra, it has found extensive application to electrochemistry, especially in studies of aromatic compounds in nonaqueous solutions. Also, electrochemical methods are particularly convenient for the generation of radical ions thus they have been used frequently by ESR spectroscopists for the preparation of samples for study. Several reviews dealing with the principles of ESR and the application to electrochemical investigations have appeared (134-138). 

Directive eSects in aromatic substitution, a quantitative treatment of, 1, 35 Carbon atoms, energetic, reactions with organic compounds, 2, 201 Electron spin resonance, identification of organic free radicals by, 1, 284 Electronically excited molecules, structure of, 1, 365... 

Controlled-potential electrolysis yields a product which may be identified in situ, e.g., spectrometrically, or after isolation from the solution. In the former case, both stable and unstable products may be studied, whereas isolation is usually limited to stable compounds. The methods used for identification of the product will also depend upon the stability of that product. Electron spin resonance, ultraviolet spectrophotometry, and cyclic voltammetry have proved useful techniques for the identification of unstable (radical) species. The presence of water in the electrolyzed solution usually prevents the use of in situ infrared (but not Raman) spectrophotometric analysis, and the use of such powerful techniques as nuclear magnetic resonance and mass spectrometry is also excluded unless the product can be isolated in a reasonably pure state. 

Electron paramagnetic resonance (EPR) spectroscopy has played a major role in the study of charged organic compounds, as it can be used in the identification of the radical anions formed [54]. The equation describing the absorption (or emission) of microwave energy between two spin states is ... 

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