Free Radical Reactions

Introduction:

• Free radical reactions are a type of chemical reaction involving highly reactive molecules called free radicals.
• Free radicals have unpaired electrons, making them highly unstable and reactive.

Formation of Free Radicals

• Free radicals can be formed through various processes, including:
  • Homolytic Bond Cleavage: When a covalent bond breaks, each atom retains one of the shared electrons, forming two radicals.
  • Initiation: The first step in a free radical chain reaction, where a molecule is split into two radicals.
  • Propagation: Radicals react with other molecules, creating more radicals and propagating the reaction.
  • Termination: The reaction stops when two radicals combine to form a stable molecule.

Examples of Free Radicals

• Some common free radicals include:
  • Hydroxyl Radical (·OH): Formed from water in the presence of UV radiation.
  • Methyl Radical (·CH₃): Produced during the combustion of hydrocarbons.
  • Chlorine Radical (·Cl): Found in the stratosphere and involved in ozone depletion.

Relevance in Chemistry

• Free radical reactions play a crucial role in:
  • Polymerisation processes (e.g., making plastics).
  • Combustion reactions (e.g., burning fuels).
  • Atmospheric chemistry (e.g., ozone depletion).

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Free Radical Reactions

Initiation, Propagation, and Termination

• In a typical free radical reaction:
  • Initiation: A molecule is broken down into two radicals, often by heat or light.
  • Propagation: Radicals react with other molecules, creating new radicals, which continue reacting.
  • Termination: The reaction stops when radicals combine to form stable molecules.

Radical Polymerisation

• Free radical reactions are essential in the production of polymers:
  • Monomers (small molecules) join together to form a polymer chain through radical reactions.
  • Initiators, such as peroxides, generate radicals to start the reaction.

Conclusion

• Free radical reactions involve highly reactive molecules with unpaired electrons.
• They have significant applications in chemistry, including polymerisation and combustion reactions, and play a role in atmospheric processes. Understanding free radicals is vital in various fields of science and industry.