The pinacol–pinacolone rearrangement is a method for converting a 1, 2-diol to a carbonyl compound in organic chemistry. The 1, 2-rearrangement takes place under acidic conditions, the name of the rearrangement reaction comes from the rearrangement of pinacol to pinacolone. This reaction was first described by Wilhelm Rudolph Fittig in 1860 of the famed Fittig reaction involving coupling of 2 aryl halides in presence of metal in dry ethereal solution. In the course of this reaction, protonation of one of the –OH groups occurs. If both the –OH groups are not alike, the one which yields a stable carbocation participates in the reaction. Subsequently, a group from the adjacent carbon migrates to the carbocation center. The driving force for this rearrangement step is believed to be the stability of the resultant oxonium ion. The migration of alkyl groups in this reaction occurs in accordance with their usual migratory aptitude, the conclusion which group stabilizes carbocation more effectively is migrated In cyclic systems, the reaction presents more features of interest.
In these reactions, the stereochemistry of the plays a crucial role in deciding the major product. An alkyl group which is situated trans- to the leaving –OH group alone may migrate, if otherwise, ring expansion occurs, i. e. the ring carbon itself migrates to the carbocation centre. This reveals another interesting feature of the reaction, viz. that it is largely concerted, there appears to be a connection between the migration origin and migration terminus throughout the reaction. Moreover, if the alkyl group has a chiral center as its key atom. Although Fittig first published about the pinacol rearrangement, it was not Fittig, in an 1859 publication Wilhelm Rudolph Fittig described the reaction of acetone with potassium metal. Fittig wrongly assumed a molecular formula of n for acetone, the result of an atomic weight debate finally settled at the Karlsruhe Congress in 1860. He wrongly believed acetone to be an alcohol which he hoped to prove by forming an alkoxide salt. The reaction product he obtained instead he called paraceton which he believed to be an acetone dimer, in his second publication in 1860 he reacted paraceton with sulfuric acid.
Again Fittig was unable to assign a structure to the reaction product which he assumed to be another isomer or a polymer. Contemporary chemists who had adapted to the new atomic weight reality did not fare better