Ozone, O3, is an allotrope of oxygen that adds rapidly to carbon-carbon double bonds.
Reactive intermediates called ozonides form from the interaction of ozone with alkenes.
These unstable compounds may be converted to stable products by either a reductive workup (Zn dust in water or alcohol) or an oxidative workup (hydrogen peroxide).
Reductive workup gives an aldehyde product when hydrogen is present on a double bond carbon atom, whereas oxidative workup gives a carboxylic acid or carbon dioxide in such cases.
Ozonide formation: a process that is believed to involve initial syn-addition of ozone, followed by rearrangement of the extremely unstable molozonide addition product.
In the reaction with ozone, carbon-carbon double bonds breaks and carbon-oxygen double bonds form in the two separate compounds.
The double bond of the original molecule is obtained by joining the carbon atoms of the two carbonyl compounds which are the final products of this reaction.
Hence ozonolysis helps in locating the double bond in the alkene.