halogenation theory with examples

1. Halogenation of Alkanes

2. • Free radical halogen reaction ( Cl2 or Br2 Only)
• Three step reaction
• 1) Initiation [Radical formation]
• 2) Propagation [Continuation]
• 3) Termination [ End of reaction]

3. • Initiation [Free radical formation]
Cl2 Cl + Cl
hr
R-O-OR
Peroxide effect
RO + RO

4. One electron reaction to use half arrow [fishhook arrow]
Two electron reaction.
Note:

5. 2. Propagation [Continuation]
CR3 Cl Cl+ Cl CR3 + Cl
Cl + H CR3 HCl +
One electron reaction to use half arrow [fishhook arrow]
CR3
a.
b.

6. • 3. Termination [End of Reaction]
Cl
Cl Cl2

7. Reaction
Br2
hr
Br + Br
1
2
34
1 mol [1eq]
molecular weight in grams
1) Nature of Compound – Cyclo alkane
2) Free radical halogen Reaction
Why - Use of Br2
3) Stability Order for free radical halogen reaction -
3o >2o >1o > . CH3 methyl radical
2 = 7
4 = 2 2
3
7
3
3 = 1
1= 3

8. Br2
hr
Br + Br
1
2
34
1 mol [1eq]
molecular weight in grams
+ HBr

9. A B
+ BA
2 electrone
more or excess of electrons
Heterolytic
A
+ BA
B
One electrone Homolytic

10. Br Br
Br
+ HBr
+ Br

11. Br2 2eq
Br
Br
1.
2.
Br2 2eq
Br
Br