"Sigmatropic shiftamers" are polymers that contain local "defects" - single or double bonds - which propagate via sigmatropic rearrangements. An example of a [3,3]-shiftamer is shown above in which a pair of parallel pi-bonds propagates via sequential boatlike [3,3]-shifts (Cope rearrangements). Since this process is predicted to occur with a low activation barrier (~15 kcal/mol) this system is expected to be fluxional at room temperature. Our search for additional [3,3]-shiftamers also led to the discovery of a new class of compounds called "sigma-polyacenes".
We have also explored additional shiftamers based on [1,5], [1,7], and [1,8] shifts of hydrogen. Several examples are shown above. We have also been interested in the relationships of transition structures for these sorts of [1,n] sigmatropic shifts to transition structures for electrocyclic reactions and to stable 3-center 2-electron carbocations.