Aromatic Character and Energy of the Five- and Seven-Membered Rings in Derivatives of Penta- and Heptafulvene Substituted in Exocyclic Position

Application of aromaticity indices to geometries of rings of eleven derivatives of fulvene, two salts of cyclopentadienyl, and nine derivatives of heptafulvene gives a coherent view in line with expectation due to the (4n + 2) rule: electron-donating substituents attached to exocyclic carbon atom in fulvenes and electron-accepting substituents attached to heptafulvenes increase significantly their aromatic character.