Sigmatropic rearrangement is a type of chemical reaction where a molecule undergoes a structural change, typically involving the migration of a sigma bond and the reorganization of pi bonds. This process allows for the formation of new molecular structures while conserving the overall number of atoms. These rearrangements are often classified into different categories based on the number of atoms involved in the migration. Common examples include the Cope rearrangement and the Claisen rearrangement, both of which illustrate how sigmatropic shifts can lead to diverse and useful organic compounds in synthetic chemistry.