between the migration origin and migration terminus throughout the reaction. Moreover, if the migrating alkyl group has a chiral center as its key atom, the configuration at this center is retained even after migration takes place. History Although Fittig first published about the pinacol rearrangement, it was not Fittig but Aleksandr Butlerov who correctly identified the reaction products involved. In an 1859 publication Wilhelm Rudolph Fittig described the reaction of acetone with potassium metal. Fittig wrongly assumed a molecular formula of (C3H3O)n for acetone, the result of a long-standing atomic weight debate finally settled at the Karlsruhe Congress in 1860. He also wrongly believed acetone to be an alcohol which he hoped to prove by forming a metal 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 (the actual pinacol rearrangement). Again Fittig was unable to assign a molecular structure to the reaction product which he assumed to be another isomer or a polymer. Contemporary chemists who had already adapted to the new atomic weight reality did not fare better. One of them, Charles Friedel, believed the reaction product to be the epoxide tetramethylethylene oxide in analogy with reactions of ethylene glycol. Finally Butlerov in 1873 came up with the correct structures after he independently synthesised the compound trimethylacetic (pivalic) acid which Friedel had obtained earlier by oxidizing with a dichromate. Some of the problems during the determination of the structure are because carbon skeletal rearrangements were unknown at that time and therefore the new concept had to be found. Butlerov theory allowed the structure of carbon atoms in the molecule to rearrange and with this concept a structure for pinacolone could be found. See also Semipinacol rearrangement Tiffeneau–Demjanov rearrangement, in which the leaving group is a diazo (from amine) rather than oxonium (from hydroxyl) Benzilic acid rearrangement References Rearrangement reactions