OxocarbeniumIonen

Oxocarbenium ions, also known as acylium ions, are a class of chemical species characterized by a positively charged oxygen atom adjacent to a carbonyl group. The general structure can be represented as R-C=O+R', where R and R' are typically alkyl or aryl groups. This structure can be viewed as a resonance hybrid of two canonical forms: one with a triple bond between carbon and oxygen and a positive charge on oxygen, and another with a double bond between carbon and oxygen and a positive charge on carbon. This delocalization of the positive charge contributes to their relative stability.

Oxocarbenium ions are highly reactive electrophiles and are important intermediates in various organic reactions. They are often generated in situ and immediately react with nucleophiles. Common methods for their generation include the reaction of carboxylic acids or their derivatives with strong Lewis or Brønsted acids, or through the dehydration of carboxylic acids. Their reactivity makes them crucial in reactions such as Friedel-Crafts acylation, where they act as acylating agents. They are also involved in the synthesis of esters, amides, and anhydrides. Due to their transient nature, their direct isolation is often challenging, but their presence and reactivity can be inferred from the products of the reactions in which they participate.