Intermediate Topic 763 of 1102 Organic Chemistry
Free Radicals
Species with an unpaired electron formed by homolytic bond cleavage.
In-depth explanation of Free Radicals
Free radicals are species with an unpaired electron, and they are formed when a covalent bond breaks symmetrically by homolysis, usually when heated or irradiated with light. Carbon radicals are planar or nearly planar and are stabilized by alkyl substitution through hyperconjugation and by delocalization over adjacent pi systems. Their unpaired electron makes them highly reactive, and they drive chain reactions in which one radical generates another. Radicals are intermediates in combustion, polymerization and free radical halogenation.
Going deeper: Free Radicals
Key ideas: Radicals have an unpaired electron, are electron-deficient with seven valence electrons on carbon, and are generated by heat, light or initiators such as peroxides. Stability order: benzyl, allyl > 3 > 2 > 1 > methyl > vinyl. Reactions proceed as initiation, propagation and termination; fish-hook arrows show single-electron movement. Radical chains can give many product molecules per photon.
Common mistakes and connections: Students use full-headed arrows for radical steps, or think radicals are charged. Another mistake is claiming radicals rearrange like carbocations, when they rarely do. Links to halogenation, the peroxide effect (anti-Markovnikov HBr), polymerization and antioxidants such as vitamin E.
Visualization of Free Radicals
Homolytic bond dissociation energies: weak bonds such as Cl-Cl and Br-Br split into radicals easily with light or heat. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The benzyl radical is stabilized by resonance because its unpaired electron is delocalized over the aromatic ring.
Frequently asked questions about Free Radicals
What is Free Radicals?
Species with an unpaired electron formed by homolytic bond cleavage.
Is Free Radicals a beginner, intermediate or advanced topic?
Free Radicals is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Free Radicals?
Study these earlier topics in Organic Chemistry first: Resonance Effect, Hyperconjugation, Electromeric Effect.
What comes after Free Radicals?
The next topics in Organic Chemistry are Carbocations and Carbanions.
Can I practise Free Radicals with quizzes?
Yes. The interactive lesson includes a self-check question on Free Radicals, and the Organic Chemistry quiz draws on every topic in this area.
Where Free Radicals fits in Organic Chemistry
Free Radicals is topic 35 of 148 in Organic Chemistry.