Aromaticity study on tria-, penta- and hepta-fulvene derivatives

Aromaticity of 70 mono-exocyclically tria-, penta- and hepta-fulvene derivatives, included H, CH3, CCH, CMe3, CN, CONH2, COCH3, CF3, CH2-, CC−, COO−, F, B(OH)2, OH, OCH3, O−, NH2, NO2, NO, NMe2, NH−, NH3+, NN+, SiMe3 substituents, are investigated using recently introduced Shannon Aromaticity (SA) index and some other geometric (HOMA), magnetic (different NICSs) and energetic (ISE) indices. Wide range of variation in these indices indicates to the considerable sensitivity of π-electron structure of a fulvene ring to the substituent. It is shown that although the obtained SA and HOMA values predict the aromatic character of the considered molecules, NICS-related indices predict a relatively high aromaticity/anti-aromaticity for all tria-/hepta-fulvenes. The best correlation is observed between the SA and HOMA indices and it is also shown that the former shows a significant correlation with the GEO part of HOMA index, which is due to bond alternation, rather than EN contribution, which is arisen from bond elongation.