Radical disproportionation

Radical disproportionation is a chemical reaction involving the transfer of atoms between two radicals to form an alkane and an alkene. This process is a subset of disproportionation reactions, which are reactions where a single reactant is simultaneously oxidized and reduced, transforming into two different products. In the context of radical chemistry, radical disproportionation is a significant pathway for the termination of radical chain processes, especially in the polymerization and combustion reactions.

Mechanism

The mechanism of radical disproportionation involves two radical species. These radicals, which are atoms or molecules with an unpaired electron, react together in a way that one radical donates a hydrogen atom to the other. This transfer results in the formation of an alkane (from the radical receiving the hydrogen atom) and an alkene (from the radical donating the hydrogen atom). The overall process can be represented as:

2R• → R-H + R=R

where R• represents the radical species, R-H is the alkane formed, and R=R is the alkene formed.

Conditions

Radical disproportionation occurs under conditions conducive to radical formation, such as high temperatures, ultraviolet light, or the presence of radical initiators. The reaction is common in the gas phase or in non-polar solvents where radical species can easily interact.

Significance

Radical disproportionation plays a crucial role in various chemical processes. In polymerization, it serves as a termination step that defines the molecular weight of the polymer. In combustion, it contributes to the complex network of reactions leading to the breakdown of organic molecules. Understanding this reaction is also essential in designing synthetic routes for organic compounds, as controlling radical processes can lead to more efficient and selective syntheses.

Examples

A classic example of radical disproportionation is observed in the decomposition of organic peroxides, where the peroxide bond breaks to form two radicals, which can then undergo disproportionation to yield alkanes and alkenes.

Related Reactions

• Combustion
• Polymerization
• Disproportionation
• Radical reactions

See Also

• Chemical kinetics
• Organic chemistry
• Reaction mechanism