Which of the following compounds is aromatic ?

Concept:

• Aromatic Compounds: Aromaticity is a property of cyclic, planar structures with a conjugated system of π electrons that follow Hückel's rule (4n + 2 π electrons) where n is a non-negative integer.

• Hückel's Rule:

  • To be aromatic, a molecule must have (4n + 2) π electrons, where n is a non-negative integer (n = 0, 1, 2, 3, ...).

  • The molecule must be cyclic and planar to allow π electrons to be delocalized over the entire ring structure.

  • Aromatic compounds exhibit enhanced stability due to the delocalized π electrons, often resulting in unique chemical and physical properties.

Explanation:

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  • _{Despite being a cyclic compound with conjugated π bonds, it has 4 π electrons, which does not satisfy Hückel's rule. Hence, it is not aromatic.}

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  • _{Cyclopentadiene itself is not aromatic, as there is carbon atom which is out of plane and does not satisfy aromaticity rule of huckel theory.}

• ​

  • Lone pair on nitrogen atom is localized and participate in the conjugation of electron in the ring making it a 6π electron system and due to this conjugation all the atoms are in plane. Thus it is aromatic.

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  • _{Cyclooctatetraene is a non-planar compound and has 8 π electrons, which does not satisfy Hückel's rule. Thus, it is not aromatic.}

Conclusion:

Among the given compounds,  is aromatic.