Ozonolysis, or ozonolysis-reduction, refers to the treatment of an alkene with ozone followed by a suitable reducing agent to break down complex double-bond-containing compounds into smaller, more easily identified products. From the identity of the products formed, it may be possible to deduce the structure of the original double-bond-containing substance. Ozonolysis will feature prominently in many of the road-map problems that you will encounter in this course.

A molozonide is an unstable, cyclic intermediate that is initially formed when an alkene reacts with ozone.

Alkenes can also be cleaved by other oxidizing agents such as potassium permanganate. However, KMnO₄ will carry the oxidation further than ozonolysis, so products can be slightly different. Note within the summary of the following reactions that ozonolysis produces aldehydes and ketones, while KMnO₄ can oxidize all the way to to carbon dioxide and carboxylic acid.

Diol cleavage is another example of a redox reaction; periodic acid, HIO₄, is reduced to iodic acid, HIO₃.