Radical Reactions
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
editFree-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:
- 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
- (a) Highly reactive chlorine radicals collide with CH4 molecules and abstract one of its H atoms, forming HCl and a methyl radical
- Generation of more free radicals via the 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)
- Termination of the chain reaction occurs upon the collision of two free radicals with the formation of a single covalent bond:
- Overall:
- The reaction does not stop at this stage. Further substitution may arise, resulting in a mixture of multi-substituted products: