Free radical halogenation....

**example of a chain reaction
**alkanes to alkyl halides

Overall reaction...

Mechanism has 3 major steps..

1. initiation step (form halogen atoms)

   weakest bond breaks first..

Bond	Bond Dissociation E
Cl-Cl	243 kJ/mol
C(sp^3)-H	438
C(sp^2)-H	464
C(sp^3)-C(sp^3)	376

2. two propagation steps (form C radicals)

For more information on radical structure and stability, see: Cradicalstructuresandstabilities-html.htm

3. three chain termination steps (remove components
   necessary for propagation)

As a result of combining two C radicals, the chlorination of methane yields a small amount of ethane. What are the products of bromination of ethane?

Regioselectivity of bromination is substantially greater than chlorination. Relative rates of R-H substitution...

X = Cl or Br	R3CH	R2CH2	RCH3
chlorination	5.2	3.9	1
bromination	1640	82	1