16.8 Sigmatropic Rearrangements

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    [1,5] Sigmatropic Rearrangement

    -1 σ is broken and 1 new σ bond is formed

    -Numerical notation indicates the number of atoms between new and old σ bonds

    [1,5] sigmatropic rearrangement

    Cope Rearrangement

    -A [3,3] sigmatropic rearrangement

    -All six atoms of the cyclic transition state are carbon atoms

    -Equilbrium favors more substituted alkenes

    cope rearrangement

    Claisen Rearrangement

    -A [3,3] sigmatropic rearrangement

    -1 atom of the cyclic transition state is oxygen

    - Occurs with allylic/vinyl or allylic/phenyl ethers

    -Equilibrium often favors C=O formation

    -allylic/phenyl ethers tautomerize to phenols

    claisen rearrangement
    claisen rearrangement with tautomerization