EC Mechanism Diethyl Maleate

Using this mechanism we may now explain the observed voltammetry shown in Fig. 7.4. 

As the scan rate is lowered, the DEM is able to isomerise to form DEF . The oxidation of DEF corresponds to the voltammetric peak at —1.36 V on the reverse scan, and hence at the intermediate scan rate (10Vs ) a mixture of products is formed by partial isomerisation, leading to two peaks being observed on the reverse scan. 

At low scan rates (0.1 Vs ) the majority of the DEM is converted to its isomer DEF before the reverse sweep, and so only one voltammetric feature is observed on the reverse scan, situated at —1.36 V. 

The DEM formed is consumed by the chemical step such that, at equilibrium, we can write 

Inspection of this equation allows us to see that as the equilibrium constant for the chemical step increases the associated equilibrium potential for the redox couple will become less negative, i.e. the species becomes easier to reduce leading to a positive shift in the voltammetric peak position. 

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