Theoretical Studies Regarding the Aromaticity of Some Non-Planar Circulenes

The aromatic character of three non-planar circulenes has been investigated at B3LYP/6-311+G(d,p) level of theory. Global aromaticity descriptors like HOMO-LUMO gap, enthalpy of formation and exaltation of magnetic susceptibility outline a possible aromatic character only for circulenes [4:64] and [7:67]. The viability of isodesmic reaction schemes -for evaluation of the enthalpies of formation- has been discussed. Local aromaticity descriptors like HOMA (Harmonic Oscillator Model of Aromaticity), NICS (Nucleus Independent Chemical Shift) and electronic delocalization indices have been calculated for each outer ring of circulenes.