Radical Reactions

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A free radical is a molecule which has an extra electron/open shell configuration. It does not satisfy the octet rule and is usually highly reactive.


Types of Radical Reactions[edit]

Free-Radical Substition[edit]

  • Reaction : CH4 + Cl2 --> CH3Cl + HCl
  • The reaction involves a chain reaction consisting of 3 steps: initiation, propagation, termination
Step 1: Initiation
Formation of the Cl· free radical via homolytic fission of the Cl-Cl bond:
Step 2: Propagation
Generation of more free radicals via the chain reaction:
(a) Highly reactive chlorine radicals collide with CH4 molecules and abstract one of its H atoms, forming HCl and a methyl radical
(b) Methyl radical produced then abstracts a Cl atom from a Cl2 molecule, chloromethane and Cl· radical
Then (a), (b), (a), (b)...
The chlorine free radical produced can attack another CH4 molecule and hence the process continues - a chain reaction
Step 3: Termination
Termination of the chain reaction occurs upon the collision of two free radicals with the formation of a single covalent bond:
(trace amount)


Overall:
  • The reaction does not stop at this stage. Further substitution may arise, resulting in a mixture of multi-substituted products: