My understanding of aromatic nature is, that the molecule must be cyclic, planar, every atom in the ring must be sp2-hybridized and the molecule must have [4n+2] π electrons, where n∈N (Hückel’s rule). The molecular orbitals also have to have the correct orientation and phase for aromaticity.
- A and B are aromatic since they follow conditions as above(including empty orbital of boron in conjugation.)
- azulene's aromaticity is due to the “fusion” of two aromatic ions, both with 6 π electrons, cycloheptatrienyl (tropylium) cation and cyclopentadienyl anion.
Based on the above My answer was a,b, and c .
Given answer : a,b,c,d.
I checked for d. It was aromatic as described in this link. 1. The diagram indicates only π electrons along the blue need to be considered amounting to 18 π electrons in conjugation.
My question is why only consider π electrons in blue and why not others? How do we explain the aromaticity of porphyrin?