(Anti)aromaticity of Cyclo[2<i>n</i>]Carbons (<i>n</i> = 3–12)

The (anti)aromaticity of the two π-systems of cyclo[2n]carbons (n = 3-12) was analyzed based on its inherent properties: molecular structure, electron delocalization, and energetic (de)stabilization. Conclusions were made based on calculated bond length and bond angle alternation (BLA and BAA), bond order (BO), energy per atom, thermodynamic stability relative to acyclic analogues, aromatic fluctuation index (FLU), electron density of delocalized bonds (EDDB), vertical resonance energy (VRE), and extra cyclic resonance energy (ECRE). It was found that rings with n = 3, 5, and 7 are doubly stabilized by aromaticity. For n = 4 and 6, the out-of-plane π-system is nearly localized with RE similar to that of acyclic analogue, but the in-plane π-system is moderately stabilized by weak delocalization. The two π-systems behave similarly starting from cyclo[16]carbon. They are nearly localized and energetically almost unaffected by (anti)aromaticity.