---
title: "Photoredox and Electrochemical Routes to Radical Intermediates"
description: "A single electron transfer makes an intermediate that two-electron chemistry cannot reach. Light absorbed by a photocatalyst and a controlled electrode potential are two ways to supply that electron, "
canonical: https://lightmysky.com/learn/science/photoredox-and-electrochemical-routes-to-radical-intermediates-mt_YhqzHGcx31
source: https://lightmysky.com/learn/science/photoredox-and-electrochemical-routes-to-radical-intermediates-mt_YhqzHGcx31.md
retrieved: 2026-09-12
---

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# Photoredox and Electrochemical Routes to Radical Intermediates

A single electron transfer makes an intermediate that two-electron chemistry cannot reach. Light absorbed by a photocatalyst and a controlled electrode potential are two ways to supply that electron, and both give the chemist a dial for how hard to push.

Subject: Science · Area: Chemistry · Ages 23 to 24
Page: https://lightmysky.com/learn/science/photoredox-and-electrochemical-routes-to-radical-intermediates-mt_YhqzHGcx31

## Ready when they can

- Reads an excited-state reduction potential and predicts whether a given substrate will accept an electron
- Distinguishes an oxidative quenching cycle from a reductive one on the order of the steps
- Explains why an electrochemical version can replace a stoichiometric oxidant and what that saves
- Names the side reaction that limits radical chemistry at high concentration

## Lesson: One electron, two ways to push it

Some reactions move one electron from a giver to an acceptor. Losing an electron is oxidation and gaining one is reduction, and the two always happen together. The giver is called the reductant and the acceptor the oxidant. That single moving electron creates a radical intermediate that two-electron chemistry cannot reach.

A photocatalyst that has absorbed light becomes much better at giving or taking a single electron. In an oxidative quenching cycle the excited catalyst gives an electron first and takes one back later. In a reductive cycle the order flips: it takes first, then gives. Reading which step comes first tells you which cycle you hold.

**Example.** To track the electrons, split the change into half-reactions, one for oxidation and one for reduction. Balance atoms and charge in each half, then recombine them. This half-reaction method is the standard tool for making sense of single-electron steps, including the potentials that say whether transfer is feasible.

**Tip.** An electrode held at a chosen potential is a tunable electron source or sink. It can replace a stoichiometric oxidant that would be used up and become waste, saving reagent and cutting waste. Run dilute so radicals meet substrate instead of each other, since crowding feeds side reactions.

**Recap.** Light or a dialled potential moves one electron; half-reactions track it and dilution protects it.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Electrode Kinetics: Exchange Current and Overpotential](https://lightmysky.com/learn/science/electrode-kinetics-exchange-current-and-overpotential-mt__z7Y780pyo)
- [What an Excited Molecule Does Next: Fluorescence and Phosphorescence](https://lightmysky.com/learn/science/what-an-excited-molecule-does-next-fluorescence-and-phosphorescence-mt_5AVF6uWed_)
- [Olefin Metathesis and Ring-Closing Strategy](https://lightmysky.com/learn/science/olefin-metathesis-and-ring-closing-strategy-mt_J9UAxKsgSk)
- [Radical Selectivity, Stability and Allylic Positions](https://lightmysky.com/learn/science/radical-selectivity-stability-and-allylic-positions-mt_tgIlRLvc9x)

## Opens up

- [Taking a Route into Flow and Onto Scale](https://lightmysky.com/learn/science/taking-a-route-into-flow-and-onto-scale-mt_eOjBPoeZSf)