Electrochemical electron spin resonance

The third area of interest has been the observation by optical and ESR spectroscopy of intermediates that are produced electrochemically. Electron spin resonance is a useful technique for identifying species that have unpaired electrons, and reviews have documented the power of ESR for unraveling complicated reaction pathways.75-77 A number of cells have been described for use with this technique that fall into two categories—the flow cell in which the reactive intermediate is generated externally and flows into the cavity78 and the in situ generation system where electrodes are placed inside the resonant cavity of the spectrometer.79... 

Goldberg, I. B. McKinney, T. M. Principles and Techniques of Electrochemical-Electron Spin Resonance Experiments. In Laboratory Techniques in Electroanalytical Chemistry, Kissinger, P. T. Heineman, W. R., Eds. Marcel Dekker, New York, 1984, Chapter 24, pp 675-728. 

ECESR Electrochemical electron spin resonance spec-... 

LB. Goldberg, D. Boyd, R. Hirasawa, A.J. Bard. Simultaneous electrochemical-electron spin-resonance measurements. 3. Determination of rate constants for second-order radical-anion dimerization. J Phys Chem. 78 295 (1974). 

Edwards two-parameter equation 549 Electrochemical oxidation of sulphides 76, 252, 253 of sulphoxides 968, 987, 1043 Electrochemical reduction of sulphones 962, 963, 1002-1041 of sulphoxides 933, 1041, 1042 Electronegativity, of the sulphur atom 584 Electronic effects 390, 484-535 Electron scavengers 892, 896 Electron spin resonance spectroscopy 874, 890-895, 1050-1055, 1082, 1083, 1090-1093... 

In the mid-1980s in situ cells were produced that showed satisfactory electrochemical behaviour, so-called simultaneous electrochemical and electron spin resonance (SEESR) techniques, and the ex situ/in situ division disappeared. A division that has remained, however, is the separation of epr approaches into those dedicated to the detection and identification of short-lived radicals and those that are capable of studying the kinetics of the decay of radicals, as well as obtaining their identity. The latter techniques are not capable of studying... 

Electrochemical methods for the generation of anion-radicals consist of potential-controlled electrolysis. The control of a potential allows one to detain rednction just after a one-electron transfer to a depolarizer. The one-electron natnre of the electron transfer is coincidentally inspected by means of coulombometry. One molecnle mnst consnme one electron. If less than one electron is consumed in the framework of the one-electron rednction, it means that the yield of an anion-radical is not quantitative. The electrolysis in a special amponle placed into a resonator of the electron spin resonance (ESR) spectrometer permits one to identify many nnstable anion-radicals. The electrochemical methods of anion-radical generation employ an electrode as an electron donor. 

Electron Spin Resonance Coupling Constants (Gauss) of Radicals of Some Aromatic Nitrocompounds, Produced Electrochemically and Photochemically, in Protic and Aprotic Media... 

The first intermediate to be generated from a conjugated system by electron transfer is the radical-cation by oxidation or the radical-anion by reduction. Spectroscopic techniques have been extensively employed to demonstrate the existance of these often short-lived intermediates. The life-times of these intermediates are longer in aprotic solvents and in the absence of nucleophiles and electrophiles. Electron spin resonance spectroscopy is useful for characterization of the free electron distribution in the radical-ion [53]. The electrochemical cell is placed within the resonance cavity of an esr spectrometer. This cell must be thin in order to decrease the loss of power due to absorption by the solvent and electrolyte. A steady state concentration of the radical-ion species is generated by application of a suitable working electrode potential so that this unpaired electron species can be characterised. The properties of radical-ions derived from different classes of conjugated substrates are discussed in appropriate chapters. 

Method. When rapid techniques are involved the following abbreviations apply F, flow TJ, temperature jump PJ, pressure jump E, electrochemical NMR, nuclear magnetic resonance ESR, electron spin resonance SA, sound absorption EF, electric field. Classical methods for investigating kinetics are not specified unless low temperatures (LT) have been used. 

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