[mana]

hi all
compare these two resonance contributor of benzo[a]pyrene! why in the first the central bond is not counted thus the first structure (18 e) is aromatic but in the second structure two carbons are not counted and the structure is antiaromatic!
can I say if a double bond is between 3 ring at least that double bond must not be counted for 4n+2 rule?

[chenbeier]

The bonds are not fixed. ech carbon is sp² hybridiziesed, so all rings also aromatic. The simplest one would be benzene with 4n +2