A 1,3-sigmatropic rearrangement is a type of chemical reaction where a sigma bond shifts between two atoms in a molecule, resulting in a new arrangement of atoms. This process typically involves the migration of a substituent across a double bond, leading to the formation of a new product while maintaining the overall molecular framework. This rearrangement is classified as a sigmatropic reaction, which is characterized by the movement of sigma bonds in a concerted manner. 1,3-sigmatropic reactions are often facilitated by heat or light and are important in organic synthesis for creating complex molecules efficiently.