1. Free Radical Chlorination

2. Experimental Evidence Helps to Determine Mechanism Chlorination does not occur at room temperature in the dark. The most effective wavelength of light is blue that is strongly absorbed by Cl 2 gas. The light-initiated reaction has a high quantum yield (many molecules of product are formed from each photon of light).

3. Free Radical Species are Constantly Generated Throughout the Reaction Propagation

4. Termination: Reaction of any 2 Radicals

5. Chlorination of Propane

6. H’s are not abstracted at the same rate. For secondary: 70%/4H = 17.5 For primary: 30%/6H = 5.0 Therefore… Relative rate of H abstraction for 1 o : 2 o is 1 : 3.5

7. Chlorination of Methylpropane

8. 3 o Radicals are Easiest to Form

9. Tertiary H’s removed five times more readily than primary H’s in chlorination reactions Relative reactivity of 1 o H abstraction: 65% / 9H = 7.2 Relative reactivity of 3o H abstraction: 35% / 1H = 35 Therefore… Relative rate of H abstraction for 1 o : 3 o 1:5

10. Stability of Free Radicals

12. Bromination is Very Selective

13. RDS in Bromination is highly endothermic

14. Consider the free radical monochlorination of 2,2,5-trimethylhexane. Draw all of the unique products (ignore stereoisomers; use zig-zag structures please) and predict the ratio or percent composition of the products. The relative reactivity of H abstraction in a chlorination reaction: 1 o : 2 o : 3 o = 1: 3.5: 5

15. 2.(12) Consider the free radical monochlorination of 1,4-dimethylcyclohexane. The reaction affords three different products (all C 8 H 15 Cl). In this reaction, the rates of hydrogen abstraction of primary : secondary : tertiary are 1 : 3.5 : 5. Draw the three products and predict the percent composition (or ratio) of the product mixture. (Disregard cis / trans isomers for this problem.)