Abstract: The transfer of oxygen atoms plays an important role in organic chemistry. Carbonyl oxides 1 and the isomer dioxiranes 2 are discussed as short-lived intermediates in decomposition processes, oxidations of organic compounds (Baeyer-Villiger Reaction, Ozonolysis), and enzymatic processes 1, 2, 3. During the last years 2 have have been used as selective oxygen transfer reagents 4, 5, 6, 7, 8, 9. A successful technique for the stabilization of reactive molecules is the introduction of sterically demanding groups such as t-butyl or mesityl. While several derivatives of dioxiranes 2 could be synthesized and characterized in solution, carbonyl oxides 1 are in general transient spezies.