In a Sigmatropic Rearrangement, one σ-bond breaks into order for another to take place elsewhere within the molecule. The term sigmatropic originates from the Greek term tropos, which means "change."

     These rearrangements come in multiple variations of patterns, some of which are;

• [1,3] Hydride Shifts
• [1,5] Hydride Shifts
  • A hydride shift refers the "shifting" of a hydride ion to another location about the molecule, whoms distance from its origin is told by out bracketed numbers.
• [1,3] Alkyl Shift
  • An alkyl shift is the "shifting" of an alkyl group rather than a hydride.
• Cope Rearrangements ([3,3] Alkyl Shifts)
  • In "Cope Rearrangements," named after Arthur C. Cope, all atoms within the rearrangement are Carbons that follow a [3,3] pattern.  This rearrangement looks extensively into 1,5-dienes.
• Claisen Rearrangements
  • Likewise to the "Cope Rearrangement," we have the "Claisen Rearrangement," named after Rainer Ludwig Claisen, where allyl vinyl ethers react in a [3,3] system.
• Oxycope Rearrangements
  •  Finally, we have the "Oxycope Rearrangement," which is almost a mix of the Cope and Claisen reactions, however, instead of an ether reacting, the molecule has an allyly hydroxyl group.

     The numbers in brackets (i.e. [x,y]) yield to the number of atoms dividing bonds in formation (x), and the number of atoms dividing bonds breaking within the pericycle transition state. So, for example, a [1,3] rearrangement has 1 bond separating the bonds in formation, and 3 bonds separating the bonds being broken.

       Now to look into some of the aforementioned reactions.