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.
wagner meerwein regrouping 01
wagner meerwein regrouping 02