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Sigmatropic Rearrangement definitions

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  • Sigmatropic Shift
    A pericyclic rearrangement where a sigma bond breaks and a new one forms, with pi bonds unchanged in number.
  • Pericyclic Reaction
    A concerted process involving cyclic redistribution of bonding electrons, often heat-activated.
  • Sigma Bond
    A single covalent bond formed by head-on overlap of atomic orbitals, broken and formed during these rearrangements.
  • Pi Bond
    A covalent bond formed by side-to-side overlap of orbitals; its quantity remains constant in these shifts.
  • Constitutional Isomer
    A compound with the same molecular formula as another but a different connectivity of atoms, resulting from the rearrangement.
  • Cope Rearrangement
    A classic example of a sigmatropic shift involving a 1,5-diene system undergoing a concerted sigma bond migration.
  • Claisen Rearrangement
    A well-known [3,3] sigmatropic shift involving allyl vinyl ethers, leading to a new carbon framework.
  • Concerted Mechanism
    A process where bond breaking and forming occur simultaneously in a single step, without intermediates.
  • Cyclic Transition State
    A transient structure where atoms are arranged in a ring during the rearrangement, facilitating electron movement.
  • Nomenclature
    A systematic method for naming these shifts, using numbers to indicate positions of bond breaking and forming.
  • Heat Activation
    A requirement for these reactions, where thermal energy initiates the concerted rearrangement.
  • Intramolecular Reaction
    A transformation occurring within a single molecule, as seen in these rearrangements.
  • [x,y] Shift
    A notation indicating the positions, counted from the broken bond, where the new sigma bond forms.