The document summarizes the Tiffeneau–Demjanov rearrangement reaction. It was discovered in the early 1900s by French chemist Marc Émile Pierre Adolphe Tiffeneau and Russian chemist Nikolay Yakovlevich Demyanov. The reaction involves treating 1-aminomethyl-cycloalkanol with nitrous acid to form an enlarged cycloketone through a 1,2-carbon migration. This ring expansion reaction is useful for increasing the size of amino-substituted cyclic compounds from four to eight-membered rings. The mechanism involves diazotization of the amine to form a diazonium ion that undergoes 1,2-alkyl shift accompanied by nitrogen loss to form