Aromaticity of annulated benzene, pyridine and phosphabenzene

Cyclopropa-, cyclopbutana-, and cyclobutena-annulated benzenes, pyridines, and phosphabenzenes are potentially aromatic compounds. The structures of all mono-, di- and tri-annulated variations are optimized at the B3LYP/aug-cc-pVDZ level. Their aromaticity is evaluated in terms of bond alternation, magnetic properties (NICS), and resonance energy. The cyclopropa systems are aromatic, the cyclobutanana systems express some aromaticity and the cyclobutena systems are not aromatic.