Radical
Definition and meaning of Radical in chemistry.
A radical is an atom or molecule with an unpaired electron. Free radicals are highly reactive intermediates that form when covalent bonds break homolytically and are central to many important chemical reactions.
In more detail
Free radicals possess a single, unpaired electron in an atomic or molecular orbital, creating an electron deficiency that drives rapid reactions with other molecules. They are typically generated through homolytic bond cleavage (symmetrical breaking requiring energy), photodissociation, or redox processes. Radicals participate in combustion, alkane halogenation, polymerization, and atmospheric chemistry. Although generally short-lived, some radicals achieve relative stability through resonance effects or steric hindrance, allowing them to be observed or even isolated. Biological radicals like the hydroxyl radical (OH•) contribute to oxidative damage in cells.
Key facts
| Field | Organic Chemistry |
|---|---|
| Key feature | Unpaired electron in valence shell |
| Notation | Shown with a dot (•) after the formula, e.g. CH3• |
| Reactivity | Extremely high; radicals quickly react to pair their unpaired electron |
When chlorine gas is exposed to ultraviolet light, homolytic cleavage produces chlorine radicals: Cl2 + hν → 2Cl•. These chlorine radicals initiate the free radical chain reaction of alkane chlorination, where Cl• abstracts a hydrogen atom from an alkane, generating an alkyl radical that continues the chain.
Frequently asked questions
How do free radicals form?
Primarily through homolytic cleavage of bonds (symmetrical breaking requiring energy input), photodissociation when molecules absorb light, or redox reactions. Thermal energy can also break weak bonds homolytically.
Why are free radicals important in chemistry?
Free radicals are intermediates in many reactions essential to industry and nature: combustion, polymerization of plastics, atmospheric ozone formation and destruction, and biological processes. Understanding radical mechanisms is fundamental to organic synthesis.