Which molecule is considered an aromatic compound?

Benzene is considered an aromatic compound because it meets the criteria established by Hückel's rule. Aromatic compounds are typically characterized by having a cyclic structure, being planar, and containing a fully conjugated ring of p orbitals that allows for delocalized pi electrons. Benzene, specifically, consists of six carbon atoms arranged in a ring with alternating single and double bonds. However, the electron structure of benzene is such that it actually exhibits resonance, leading to equal bond lengths and a stable, planar structure.

Moreover, benzene has a total of six pi electrons (one from each carbon in the ring), aligning perfectly with Hückel's rule, which states that a cyclic, planar molecule is aromatic if it contains ( 4n + 2 ) pi electrons, where ( n ) is a non-negative integer. For benzene, ( n = 1 ) results in ( 4(1) + 2 = 6 ) pi electrons, confirming its aromaticity.

In contrast, the other options are not aromatic due to their structural characteristics: cyclohexane is a saturated hydrocarbon with single bonds only and does not have the delocalized pi electron system required for aromaticity;