Möbius pi-bond shifting has been identified as a mechanism for thermal configuration change in annulenes. Given that heavy atom tunneling plays a role in planar bond shifting in cyclobutadiene, we explored the contribution of heavy-atom tunneling in the Möbius pi-bond shifting in [12]-, [14]- and [16]annulene. Tunneling in these systems would involve all carbons simultaneously. Intrinsic reaction coordinate calculations using BHandHLYP/cc-pVDZ and M06-2X/cc-pVDZ levels of theory reveal relatively narrow barrier widths and suggest a high probability of tunneling for Möbius pi-bond shifting in [12]-, [14]- and [16]annulene. Small curvature tunneling (SCT) calculations predict that carbon tunneling dominates the Möbius pi-bond shift in [16]annulene at temperatures from 10 K to 250 K. At 160 K tunneling is predicted to account for 99% of reaction, and the predicted half-life is ca. 4 seconds.

Computational study of heavy-atom tunneling in the Möbius pi-bond shifting in [4n]- and [4n+2]annulenes

255th National Meeting (2018)

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