1. Alkanes Principle reaction type: free radical substitution
Mechanism: (chain reaction) substitution

2. Free radical substitution
chlorination of methane
i.e. homolytic breaking of covalent bonds
Overall reaction equation
CH4 + Cl2
CH3Cl + HCl
Conditions
ultra violet light
excess methane
to reduce further substitution

3. Free radical substitution mechanism
ultra-violet Cl
Cl Cl
initiation step
H3C H Cl
H3C
H Cl
two propagation steps
H3C
Cl Cl
H3C Cl Cl
H3C Cl
H3C Cl
termination step
minor termination step
H3C
H3C CH3
CH3

4. Further free radical substitutions
Overall reaction equations
CH3Cl + Cl2
CH2Cl2 + HCl
CH2Cl2 + Cl2
CHCl3 + HCl
CHCl3 + Cl2
CCl4 + HCl
Conditions
ultra-violet light
excess chlorine