Recent computational work has suggested that medium-sized annulenes undergo facile thermal configuration change by p-bond shifting via H�ckel and M�bius topologies. The observations concerning mechanisms and topology in these species warrants exploration in the closely related dehydroannulenes. Reinvestigation of the isomerization of dehydro[10]annulene from its mono-trans global minimum (CTCC) to its all-cis configuration (CCCC) shows a one-step process through a M�bius bond-shift transition state, with a barrier at least 9 kcal/mol lower than those computed for previously located mechanisms. In addition, the isomerization of CCTCTC to CTCCTC dehydro[14]annulene -- a reaction observed by Sondheimer -- occurs via two H�ckel-topology bond shifts. Analysis of C-C bond lengths as a function of reaction coordinate in these isomerization pathways demonstrates that p-bond shift midpoints do not necessarily correspond to transition states. In fact, p-bond shifting can occur quite close to the minima involved in the reaction.

Circuital patterns: Pi-bond-shifting in medium-sized dehydroannulenes via Mobius and Huckel topologies

245th National Meeting (2013)

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