A 1,5-sigmatropic rearrangement is a type of chemical reaction where a sigma bond shifts between two atoms in a molecule. This process involves the migration of a substituent from one carbon atom to another, typically involving a cyclic transition state. In this rearrangement, the movement occurs over a five-membered ring, which includes the original and the new positions of the substituent. Sigmatropic rearrangements are important in organic chemistry as they can lead to the formation of new compounds and are often used in synthetic pathways.