Question

What is meant by the statement: An inner sphere electron transfer process cannot occur faster than the slowest substitution process for both the reductant and the oxidant.

Answer 1

This statement is related to electron transfer reactions of metal complexes.

There are 2 types of electron transfer reaction mechanisms.

1. outer-sphere mechanism and 2. inner sphere mechanism.

In Outer-sphere mechanism, the duration of interaction, between oxidizing and reducing agent during electron transfer, is very small.

Whereas, in Inner-sphere mechanism, the oxidizing and reducing agents forms an activated complex during electron transfer. At least one ligand belonging to the coordination shell will be in contact with the activated complex. These ligands help in the transfer of electrons.

If we compare the rate of the above electron transfer process (inner sphere mechanism) to any other substitution reactions of (the same) reductant or oxidant, the rate of electron transfer is very slow.

The latter statement is explaining the rate of electron transfer reaction and stressing that it is very slow comparing it to the slowest substation reaction.