A Level Radical Reactions

Synthesis of Chloroalkanes

Click the structures to view the separate chain reaction steps in more detail

Chloroalkanes are alkanes with one or more hydrogen atoms substituted by a chlorine atom.

Halogens react with alkanes in photochemical reactions to form haloalkanes. Photochemical reactions are started by ultraviolet light. A hydrogen atom is substituted by chlorine. This is a free radical substitution reaction.

Free radicals are molecules with an unpaired electron, written like Cl• or CH3•. Free radicals are highly reactive and the result of bonds splitting equally - initiation reaction.

The reaction mechanism for the synthesis of chlormethane is shown above and happens when a mixture of methane and chlorineare exposed to UV light. The overall equation is: CH4 + Cl2 -> CH3Cl + HCl

The reaction mechanism shows each step in the synthesis, in this case the free radical chain reaction has three stages - initiation, propagation and termination.

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