Radical Formation: Overview

Radicals form from spin-paired molecules through homolysis or electron transfer. Homolysis breaks a bond to create two radicals, represented by a fishhook arrow showing single electron motion. Electron transfer, also called reduction, adds an electron to a spin-paired molecule to generate a radical.

In radical substitution or abstraction, a radical interacts with a spin-paired molecule, typically abstracting a hydrogen or halogen atom. This interaction produces a new spin-paired molecule and a different radical. The process allows radicals to transfer reactivity between molecules while maintaining the total number of radicals in the system.

When a radical adds to an alkene's pi bond, it produces a carbon-centered radical. This addition method generates a new radical from the starting radical and unsaturated compound. The resulting carbon-centered radical can then participate in subsequent radical reactions or chain propagation steps.

Radical elimination is the reverse of radical addition. While addition forms a carbon-centered radical from a radical and an alkene, elimination breaks a radical compound to yield a new radical and an unsaturated compound with a pi bond. Both processes interconvert radicals and unsaturated molecules.

Homolytic bond cleavage breaks a bond to form two radicals, each receiving one electron from the broken bond. Heterolytic bond cleavage, by contrast, forms ions by unequally distributing electrons. A fishhook arrow represents homolytic cleavage, distinguishing it from heterolytic processes that generate charged species.

Yes, radicals form from other radicals through three mechanisms: substitution or abstraction, addition, and elimination. In each case, one radical and one spin-paired molecule interact to produce either a new radical or spin-paired molecule and a radical. These pathways enable complex radical chain reactions.

Electron transfer, or reduction, adds an electron to a spin-paired molecule to create a radical. Unlike homolysis, which generates two radicals from one molecule, electron transfer produces a single radical by introducing an additional electron. This method provides an alternative route to radical formation from neutral compounds.