Guilford Techno Consultants, Inc

Sunday, September 10, 2023 by Guilford Techno Consultants, Inc. | Alkene Reactions

For whatever reason, alkene reactions and their mechanisms are my favorite topics from the first semester. Although these reactions involve a large number of reagents and can be mechanistically complex, I find them much more straightforward than substitution and elimination reactions. From a mechanistic point of view, substitution and elimination reactions aren’t very complicated but there are so many moving parts to these reactions that I always feel like I’m guessing at what the products should be. Although there are quite a number of alkene reactions, I find product prediction to be fairly manageable. I also find alkene reaction mechanisms to be fairly intuitive with a few exceptions, ozonolysis being one of them.

The sigma and pi bonds of alkene double bonds can be oxidatively cleaved to yield two carbonyl groups as aldehydes or ketones depending on the structure of the alkene. One way of achieving this is through reaction of an alkene with ozone, O₃, followed by a mild reducing step to yield product. Dimethyl sulfide (DMS) and zinc in water are commonly used as reductants. Initially, ozone adds to the alkene double bond to form a five-membered ring called a molozonide. The molozonide is unstable and rearranges through a two step process to yield an ozonide, which is then treated with a reductant to produce the final products. The mechanism for the formation of the ozonide and its reduction by DMS can be found in the following presentation. Practice problems are also included.

Click Here for Ozonolysis of Alkenes