Effective concentration electron sink

Phenols are normally resistant to reduction as a consequence of ionization. This property was put to good effect in the reduction of 7-methoxyfluoren-2-ol (59 Scheme 8). Because the phenoxide ring does not serve as an electron sink, the 5,8-dihydro derivative is formed, while the styrenic double bond is protected from reduction. However, phenols have been reduced with concentrated solutions of lithium... 

The affinity generated by a concentration difference can also generate an EMF. A simple example of a CuCl2 concentration cell in which a concentration-driven EMF can be realized is shown in Fig. 10.7. In this cell the membrane is permeable to Cl but not to Cu. Two copper rods are placed in the two chambers, a and p, which become a source and a sink for the Cu " ions. The concentration difference drives Cl ions from a to p. The flow of Cl ions generates a potential difference "(as in the case of membrane potential), but due to the presence of copper rods, this potential can drive electrons from the copper rod in P to the copper rod in a, thus generating Cu ions in p and neutralizing Cu ions to Cu atoms in a. The overall process is an effective transport of Cu " " ions from a to p. The system finds a way to reach equilibrium through the flow of electrons. For a concentration cell, Vo = 0. because the standard states for the reactant and the product are the same the only difference between the two is in their activities (which nearly equal the molalities in dilute solutions). It... 

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