Oxidations and Polymerizations of Alkenes

From the mechanism of catalytic hydrogenation we notice that hydrogen adds to the alkene molecule in such a way that both H-atoms are added to the same side of the molecular plane. The stereochemistry of this reaction is called syn-addition. Addition of halogen follows qnite different stereochemistry two halogen atoms approach the alkene molecular plane from the opposite sides. Such stereochemistry is called anrt-addition. The mechanism is confirmed by the analysis of configurations of products of addition of chlorine to cyclopentene. 

In previous sections we have mentioned that oxidation in organic chemistry includes the removal of hydrogen or the addition of oxygen. Alkenes can easily be oxidized in a reactions with ozone, O3. The reaction mechanism involves the formation of a reactive intermediate, the ozonide, which subsequently decomposes into two molecules that can be either aldehydes or ketones, depending on the structure of the starting alkene (see the next scheme). 

Alkenes can also be oxidized by other reagents such as KMn04. 

Under high pressure and temperature and in the presence of oxygen or peroxides, ethene is transformed into a solid elastic substance in which the molecules are connected in long carbon chains. This product is called polyethylene and the process is polymerization. Polymerizations of alkenes are important processes for the industrial production of different technological materials. 

The types and properties of polymeric materials being formed depend on the starting molecule, the monomer and on the conditions of polymerization. Almost all industrial polymerizations require the use of an appropriate catalyst. Some polymers and starting monomers are listed in the following scheme. 

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