Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect

Very good dependences of the variation in π-electron delocalisation expressed by the aromatic character of the ring, defined by the geometry-based HOMA model and NICS index in mono 6-substituted fulvene and 8-substituted heptafulvene derivatives on the nature of substituent allows us for defining the substituent through resonance effect (by means of σp+ and σp− scale of the substituent effect). The analysis is based on 35 optimised systems at DFT B3LYP/6-311+G** level of theory.