The Addition of Ozone to an Alkene Ozonolysis

When an alkene is treated with ozone (O3) at a low temperature, both the cr and tt bonds of the double bond break and the carbons that were doubly bonded to each other are now doubly bonded to oxygens instead. This is an oxidation reaction—called ozonolysis— because the number of C—O bonds increases. 

Ozonolysis is an example of oxidative cleavage—an oxidation reaction that cleaves the reactant into pieces (lysis is Greek for breaking down ). 

a major constituent of smog, is a health hazard at ground level, increasing the risk of death from lung or heart disease. In the stratosphere, however, a layer of ozone shields the Earth from harmful solar radiation. 

The product is a ketone if the sp carbon of the alkene is bonded to two carbon-containing substituents the product is an aldehyde if one or both of the substituents bonded to the sp carbon is a hydrogen. 

The following are additional examples of ihe oxidative cleavage of alkenes by ozonolysis. (Many organic reactions that need to be carried out in the cold are done conveniently at -78°C, because that is the temperature of a mixture of dry ice—solid CO2— in acetone.) 

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