Reactions

First, the peracid acts as a nucleophile and its proximal oxygen atom attacks the electrophilic carbonyl carbon of the ketone, forming a tetrahedral intermediate. Then, with the departure of the carboxylate as leaving group, one of the C–C bonds migrates antiperiplanar to the O–O bond, which breaks heterolytically. This concerted [1,2]-shift inserts an oxygen into the C–C bond. Finally, a proton transfer yields the ester (or lactone if the substrate is cyclic). It is important to note that not all substituents migrate equally. The group that migrates is the one better able to stabilize a partial positive charge in the transition state (Tertiary alkyl > Secondary alkyl > Aryl > Primary alkyl). For aldehydes, the H always migrates, giving a carboxylic acid.