free radical chlorination n.
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Free Radical Chlorination. 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.

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experimental evidence helps to determine mechanism
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 Cl2 gas.
  • The light-initiated reaction has a high quantum yield (many molecules of product are formed from each photon of light).
h s are not abstracted at the same rate
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 1o : 2o is

1 : 3.5

tertiary h s removed five times more readily than primary h s in chlorination reactions
Tertiary H’s removed five times more readily than primary H’s in chlorination reactions

Relative reactivity of 1o H abstraction:

65% / 9H = 7.2

Relative reactivity of 3o H abstraction:

35% / 1H = 35

Therefore…

Relative rate of H abstraction for 1o : 3o

1:5

slide14

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: 1o: 2o: 3o = 1: 3.5: 5

slide15

2.(12) Consider the free radical monochlorination of 1,4-dimethylcyclohexane. The reaction affords three different products (all C8H15Cl). 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.)