Aromaticity and Mobius Antiaromaticity in Monocyclic [11]Annulenium Cations

摘要

Monocyclic [11]annulenium cations,which are experimentally unknown,have been studied primarily via DFT methods but also with some CCSD(T) validation.We have located six minima:two doubly trans (26,27),one triply trans (28),one singly trans (29),one quintuply trans (trannulene-type,33),and one all-cis (31).The first three are aromatic,33 is modestly aromatic,29 is nonaromatic,and the last is a Mobius antiaromatic species.We also investigated the fusion of various numbers of three-membered rings (3MRs) to the central 11-membered ring (11MR).We found several planar,all-cis-[11jannulenium ion derivatives as well as another Mobius antiaromatic species (52b);for comparison,we also found planar,antiaromatic all-cis-[12]annulene (60) and [15]annulenium cation (61) derivatives.The (anti)-aromatic characterization of these compounds is based mainly on calculated magnetic data for the ground singlet and vertical triplet states,although aromatic stabilization energies (ASE) are also considered.Data for optimized triplets,several of which are Mobius aromatic systems (31t,52t,63t,64t),are also included.Several of these cations are reasonable synthetic targets.