the ketone reacts with hydrogen peroxide or a peracid to form the ester . The oxidant inserts an oxygen atom between the carbonyl carbon and its neighbor (alpha carbon).

Cyclic ketones produce lactones by Baeyer-Villiger oxidation.

In the case of substituted ketones, oxygen enters from the side with more substituents.

The reaction of aldehydes with peracids produces carboxylic acids.