The above cyclobutene heterocyclic structure has been debated in regards to its aromaticity. Some argue that due to it not being able to adopt a resonance structure where each atom can be considered sp 2 -hybridized (strictly under the inclusive approach), it lacks a conjugated pi system and should be considered nonaromatic. According to David Klein's Organic Chemistry, 4th Edition 6 , though, the compound is considered aromatic even though it fails to form a valid resonance structure supporting the presence of a conjugated pi system under the inclusive approach. The reason behind its aromaticity is the nitrogens have delocalized lone pairs, so they can technically adopt an sp 2 -hybridized state (under the non-inclusive approach specifically; 3 sigma bonds + 0 localized lone pairs = 3, sp 2 ) thus making their lone pairs occupy a p-orbtial, which would form a continuous system of overlapping p-orbitals (conjugated pi system) and make the compound have 6 pi electrons (2 from the pi bond and 4 from the delocalized lone pairs on the nitrogen atoms). Since 6 is a Huckel number, the compound meets all the requirements to be considered aromatic.