Page 105 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

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Encyclopedia of Physical Science and Technology EN005F-213 June 15, 2001 20:32

Electron Transfer Reactions

Gilbert P. Haight, Jr.
University of Washington

I. Electron Transfer and Oxidation–Reduction
II. Electron Transfer from Metals to Aqueous H +
III. Atom Transfer versus Electron Transfer
IV. Electron Transfers between Pairs of Atoms:
Numbers of Electrons
V. Inner Sphere and Outer Sphere Transfers
VI. Classification of Electron Transfer Steps
VII. Pathways among Oxidation States
VIII. Electron Transfer in Biological Systems

GLOSSARY often with an open site for ligation to small molecules
capable of penetrating a hydrophobic pocket.
Bridging ligand Atom, molecule, or ion capable of co- Hole An active site in an intramolecular electron transfer
ordinating to both oxidizing and reducing agents and system with the potential to accept an electron from a
mediating electron transfer between them; such a reac- donor site.
tion is called an inner sphere electron transfer. Iron–sulfur “cubes” Clusters involved in biological
Cooxidation Three-electron transfer process involving electron transfer in a number of enzyme systems.
two electron donors; it may occur when both oxalate Multielectron, multipath systems Activated states in
and alcohol are ligated to Cr(VI) in an activated state which more than one electron may be transferred by
and are cooxidized as they transfer three electrons more than one orbital pathway in a fairly simple redox
to Cr. reaction such as cooxidation.
Electron transfer reaction Chemical reaction in which Outer sphere electron transfer Electron transfer that
there is a net loss of electrons from one or more atoms occurs when electrons pass between two centers that
or molecules accompanied by a corresponding gain of retain their coordination spheres throughout the trans-
electrons by other atoms or molecules in a system, fer process and are not joined by bridging atoms or
as when nonmetal atoms receive electrons from metal molecules.
atoms to form salts. Oxidizing agent Atom or molecule (e.g., a nonmetal
Heme iron centers Redox centers in biological systems atom) that undergoes reduction when it gains electrons
that contain iron(II) or iron(III) in a porphyrin ring, from a reducing agent.

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