Download e-book for iPad: Advances in Heterocycling Chemistry. Vol. 32 by Donald Bethell

By Donald Bethell

ISBN-10: 0080493424

ISBN-13: 9780080493428

ISBN-10: 0120335328

ISBN-13: 9780120335329

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A modified version of (18)] to give the temporal variation of the concentration of a species in an electrode reaction mechanism. In order to model the voltammetric response associated with this mechanism, a knowledge of E0f , ␣, k0 and k is required, or deduced from a theoretical–experimental comparison, and the set of concentration– time equations for species A, B and C must be solved subject to the constraints of the Butler–Volmer equation and the experimental design. Considerable simplification of the theory is achieved if the kinetics for the forward and reverse processes associated with the E step are fast, which is a good approximation for many organic reactions.

If a cation is oxidized at a positively charged electrode the current measured will decrease from the diffusion only value and Fig. 10 shows an idealized example under microelectrode steady-state Fig. 10 Steady-state sigmoidal-shaped voltammograms obtained in the presence and absence of electrolyte for the oxidation of A2ϩ to A3ϩ (adapted from Oldham, 1992). MODERN VOLTAMMETRY 21 conditions with and without added electrolyte for the one-electron oxidation of species A2ϩ to A3ϩ (which has a counter anion XϪ) (Oldham, 1992).

The peak currents Ired and Iox P P (note the baselines from which they are measured in Fig. 14). For a reversible process at 25ЊC, the value of the peak current, in amps, is given by (35). 69 ϫ 10 )n ADA ␯ [A]0 (35) This expression applies regardless of the diffusion coefficients of A and B. The increase in current with scan rate may be explained by the fact that as the scan rate increases, less time is available for the Nernst diffusion layer to relax into the solution by diffusion. Consequently, as the scan rate increases, the rate of change of concentration of A at the electrode surface increases, resulting in a greater flux of A to the electrode surface and hence a larger observed electrode current.

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Advances in Heterocycling Chemistry. Vol. 32 by Donald Bethell


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