Electron transfer

Electron transfer is a process where an electron moves from one atom, ion, or molecule to another. This movement is very important because it explains how electrons are transferred in reactions called redox reactions.

Many important natural and industrial processes depend on electron transfer. For example, it is part of electrochemical processes, which include things like batteries. Electron transfer is also important in photosynthesis and respiration, which are how plants make food and how living things get energy.

In organic chemistry, electron transfer plays a role in some reactions used to make new materials. It is also a key part of photoredox catalysis, a modern way to speed up chemical reactions using light. Understanding electron transfer helps scientists and engineers improve many technologies and understand nature better.

Classes of electron transfer

Inner-sphere electron transfer

Main article: Inner-sphere electron transfer

In inner-sphere electron transfer, two parts that can change their charge are connected by a bridge when the transfer happens. This bridge can be permanent, meaning the transfer is within the same molecule. More often, the bridge only forms right before the transfer and then breaks away afterward. A well-known example is when a special chloride piece links two different chemicals during the transfer.

Outer-sphere electron transfer

Main article: Outer-sphere electron transfer

In outer-sphere electron transfer, the parts that change their charge are not connected by a bridge. Instead, the electron moves through space from one to the other. This can happen between different chemicals or between the same type of chemical in different states. A good example is a reaction between permanganate and its reduced form.

Outer-sphere electron transfer usually happens when the chemicals don’t change shape easily or when there’s no good bridge to help the transfer.

Five steps of an outer sphere reaction

1. The chemicals come close together, forming a group => precursor complex
2. The bonds and surrounding material change shape => activated complex
3. The electron moves
4. The bonds and surrounding material settle back => successor complex
5. The products move apart

Heterogeneous electron transfer

In heterogeneous electron transfer, an electron moves between a chemical in liquid and the surface of a solid like a semi-conducting material or an electrode. This is important for electrochemistry and making solar cells.

Vectorial electron transfer

In proteins, electrons often move from one spot to another in a line. This path helps the electron travel through materials that normally don’t conduct electricity well. Common spots for these electrons are iron-sulfur clusters, and they are usually just the right distance apart for fast transfer.

Theory

The first accepted idea about how electrons move between atoms was created by Rudolph A. Marcus, who won a Nobel Prize in Chemistry in 1992. His work focused on a special type of electron movement called outer-sphere electron transfer. Later, Noel Hush and Marcus expanded this idea to include inner-sphere electron transfer, creating what is now known as Marcus-Hush theory. These theories help scientists understand how electrons move in chemical reactions. Over time, other scientists like Joshua Jortner have used even more detailed science to study this process, looking at how tiny particles like electrons behave. In proteins, the way electrons move depends on the structure of the protein bonds, almost like electrons moving through a tunnel.