In 1899, Wagner and Brickner observed a regrouping when treating a-pinene with hydrochloric acid. This observation contradicted the classical theory that was based on the invariance of the skeleton of the molecule.
In 1922, H. Meerwein established a cationic mechanism that explained the reaction. This mechanism occurs with the formation of a carbocation that undergoes a [1,2] rearrangement of hydrogen, alkyl or aryl groups.
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Mechanism:
wagner meerwein regrouping 02