Advices For Studying Organic Chemistry

H 2 CCHCH 3 Br
H Br −
H CH 2 C+HCH 3 H CH 2 CHCH 3
Br
More stable carbocation Markovnikov product

2. In the presence of peroxides, the reagent that attacks the double bond first is the
   larger bromine atom.

1. Bromine attaches itself to the less hindered carbon atom by a radical mechanism
   to form the more stable radical intermediate ⇒ anti-Markovnikov addition.
   Radical addition
   Br
   H 2 CCHCH 3 Br CH 2 CHCH 3 H Br Br CH 2 CHCH 3
   H

+ Br

More stable radical anti-Markovnikov product
4-23-02

10.10 RADICAL POLYMERIZATION OF ALKENES:

CHAIN-GROWTH POLYMERS

1. Polymers, called macromolecules, are made up of many repeating subunits
   (monomers) by polymerization reactions.

1. Polyethylene (PE):

m polymerization CH 2 CH 2 ( )CH 2 CH 2 n CH 2 CH 2

Ethylene Polyethlene

Monomeric units

(m and n are large numbers)

H 2 CCH 2

monomer polymer

2. Chain-growth polymers (addition polymers):
   
   
   1. Ethylene polymerizes by a radical mechanism when it is heated at a pressure of
      1000 atm with a small amount of an organic peroxide.
   
   
   2. The polyethylene is useful only when it has a molecular weight of nearly
      1,000,000.
   
   
   3. Very high molecular weight polyethylene can be obtained by using a low
      concentration of the initiator ⇒ initiates the polymerization of only a few chains
      and ensures that each will have a large excess of the monomer available.