Identify the aromatic compound:
Identify the aromatic compound:
The correct option is B
There is extended conjugation throughout the molecule. All carbon atoms could be regarded to have an sp2 hybridization. So we can definitely make a case for azulene to be aromatic. Also, the number of π electrons are 10 which conforms to the formula of (4n+2), where n = 2. Azulene is usually viewed as resulting from the fusion of cyclopentadiene and cycloheptatriene rings. Like naphthalene and cyclodecapentaene, it is a 10 pi-electron system. In view of the following observations, it exhibits aromatic properties:
(i) the peripheral bonds have similar lengths
(ii) it undergoes Friedel-Crafts-like substitutions.
Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula C8H6. It is antiaromatic, because it has 4n π electrons where n is any integer. For this reason it dimerizes even at temperatures as low as −100 °C.
The hydrocarbon obtained by formally cross-conjugating two cyclopropene rings through a common exocyclic double bond is called triafulvalene. It hasn't yet been synthesized. Hence, it is not known to exhibit aromatic properties. The first compound clearly violates one of Huckel's rules - where one carbon is not sp2 (it doesn't have a pure p-orbital). No delocalization over the whole ring.
There is extended conjugation throughout the molecule. All carbon atoms could be regarded to have an sp2 hybridization. So we can definitely make a case for azulene to be aromatic. Also, the number of π electrons are 10 which conforms to the formula of (4n+2), where n = 2. Azulene is usually viewed as resulting from the fusion of cyclopentadiene and cycloheptatriene rings. Like naphthalene and cyclodecapentaene, it is a 10 pi-electron system. In view of the following observations, it exhibits aromatic properties:
(i) the peripheral bonds have similar lengths
(ii) it undergoes Friedel-Crafts-like substitutions.
Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula C8H6. It is antiaromatic, because it has 4n π electrons where n is any integer. For this reason it dimerizes even at temperatures as low as −100 °C.
The hydrocarbon obtained by formally cross-conjugating two cyclopropene rings through a common exocyclic double bond is called triafulvalene. It hasn't yet been synthesized. Hence, it is not known to exhibit aromatic properties. The first compound clearly violates one of Huckel's rules - where one carbon is not sp2 (it doesn't have a pure p-orbital). No delocalization over the whole ring.
