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Figure 4.14 Anodic shift of reduction potential
owing to coordination with Lewis acid and
hydrogen bonding
It is also known that the second reduction
potentials of diketones like anthraquinone and
dinitrobenzenes shift greatly in the positive
direction in the presence of alcohols. This is due
to the formation of hydrogen bonds between
dianion
intermediates
generated
by
two-electron reduction and the alcohols.
4.5.4 Electroauxiliaries Based on
Intramolecular Coordination Effects
If a substrate molecule has a specific
coordinating site such as a functional group or
heteroatom to stabilize the electrogenerated
ionic intermediate, the electron transfer is
enhanced by intramolecular coordination, as
shown in Figure 4.15 . As such a functional
group, pyridyl, carbonyl and ether groups are
effective, and they decrease the oxidation
potential appreciably. Such coordination would
facilitate subsequent chemical steps like bond
fission. When bond cleavage accompanies
electron transfer, as shown in Figure 4.15 , the
oxidation potential decreases significantly. This
is quite a new concept and methodology for
electron transfer control [26]. Furthermore, it
has been demonstrated that a combination of
the orbital interaction and intramolecular
coordination is highly effective for controlling
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