Identifying Non-Aromatic Compounds

Aromatic compounds are characterized by their unique stability and electronic structure. When analyzing a compound like benzene (C6H6), one observes its resonance stabilization and the rule of Huckel, which states that a planar cyclic compound with 4n+2 π electrons is aromatic, where n is a non-negative integer. consider the following compounds:

(1) Naphthalene (C10H8)

(2) Cyclohexene (C6H10)

(3) Toluene (C7H8)

(4) Cyclobutadiene (C4H4)

The task is to identify which of the compounds listed above is not considered aromatic.