Symmetry restrictions as starting point for the determination of geometric representations and the dynamics of cyclic π systems

A quasiclassical‐state approach was developed for probing π bonding and delocalization energies focused on benzene. A more general picture is now given for neutral n π‐conjugated cyclic systems with a geometry distortion from D_nh into D_1/2nh (n=4,6,8,…,16), which results in a new aromaticity‐antiaromaticity criterion. For n=6 and 8 the corresponding divalent charged systems were studied in relation to zero‐field splittings of the triplet ground state and geometry, respectively. Attention is also given to antiaromatic π‐conjugated systems focused on the cyclopropenyl anion, the cyclopentadienyl cation, and the cycloheptatrienyl anion and their relaxed states. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 641–650, 2000