Ozonolysis: alkene or alkyne is cleaved by reacting it with ozone Example: *Mechanism: O3 ----------> syn addition of O3 Neither Markovnikov nor anti- Markovnikov (O3 is symmetrical) Neither alkene nor O3 is electrophile (both give and receive electrons) ------------> Oxygen lone pairs repel causing molecule to break apart and rearrange (CH3)2S --------> Final stereochemistry: Neither syn nor anti Overall mechanism: Syn addition of O3 ---> Rearrange ---> Add (CH3)2S ---> Final product cleaved by ozone *Useful tip: the products can be found (without going through the mechanism) by slicing the alkene and adding oxygen to the ends of the open alkene