The Pinacol-Pinacolone Rearrangement is an organic reaction that involves the acid-catalyzed rearrangement of a 1,2-diol pinacol to a ketone pinacolone . The reaction was first reported by Wilhelm Rudolph Fittig in 1860. The mechanism of the Pinacol-Pinacolone Rearrangement is as follows:1. Protonation: The reaction starts with the protonation of the hydroxyl group of the 1,2-diol by a strong acid, such as sulfuric acid H2SO4 or hydrochloric acid HCl . This step generates an oxonium ion.2. Rearrangement: The oxonium ion undergoes a 1,2-methyl or alkyl shift, which involves the migration of a methyl or alkyl group from one carbon to the adjacent carbon bearing the oxonium ion. Simultaneously, a hydride ion H- from the adjacent carbon is transferred to the oxonium ion, resulting in the formation of a carbocation.3. Deprotonation: Finally, a water molecule or another base deprotonates the carbocation, leading to the formation of the ketone product pinacolone .Example of the Pinacol-Pinacolone Rearrangement:Consider the reaction of pinacol 1,2-dimethyl-1,2-ethanediol with sulfuric acid H2SO4 :1. Protonation: Pinacol is protonated by H2SO4, forming an oxonium ion.2. Rearrangement: A methyl group migrates from one carbon to the adjacent carbon bearing the oxonium ion, and a hydride ion is transferred to the oxonium ion, forming a carbocation.3. Deprotonation: A water molecule deprotonates the carbocation, resulting in the formation of pinacolone 3,3-dimethyl-2-butanone .Overall, the Pinacol-Pinacolone Rearrangement converts pinacol 1,2-dimethyl-1,2-ethanediol to pinacolone 3,3-dimethyl-2-butanone in the presence of a strong acid.