Abstract: Carbonyl oxonium intermediates are highly reactive and prone to a variety of reactions. This paper outlines five key types of reactions involving carbonyl oxonium intermediates in university-level organic chemistry education: addition, substitution, decomposition, isomerization, and pericyclic reactions. The role of carbonyl oxonium as a crucial intermediate in the mechanisms of complex organic reactions is discussed. It is important to note that the reactivity of carbonyl oxonium is multifaceted and subject to competition and coexistence among these different reaction types. A thorough understanding of these five reactions enhances scientific reasoning and literacy in organic chemistry, aligning with the educational philosophy that “organic chemistry is both a science and an art”.

Key words: Organic chemistry, Carbonyl group, Oxonium, Reaction mechanism