This observation can be explained on the basis of Hückel's rule.

It is the theoretical basis for the Hückel's rule.

Indeed, Hückel's rule can only be theoretically justified for monocyclic systems.

Some porphyrin derivatives follow Hückel's rule, but most do not.

This ion is predicted to be aromatic by Hückel's rule.

This hydrocarbon obeys Hückel's rule and is, therefore, an aromatic compound.

Although the Hückel's rule cannot be strictly applied to borole, it is considered to be anti-aromatic.

This is known as Hückel's Rule.

In organic chemistry, Hückel's rule estimates whether a planar ring molecule will have aromatic properties.

The fused ring system therefore contains a total of ten pi electrons and hence according to Hückel's rule is aromatic.

Antiaromatic compounds fail Hückel's rule of aromaticity i.e. 4n+2 pi electrons.

Some non-benzene-based compounds called heteroarenes, which follow Hückel's rule, are also aromatic compounds.

Hückel's rule is not valid for many compounds containing more than three fused aromatic nuclei in a cyclic fashion.

Conjugated, planar, cyclic compounds that follow Hückel's rule are aromatic and exhibit an unusual stability.

The dianion, however, satisfies Hückel's rule, is thermally stable, and is planar.

The rule that excess electrons in the ring produces an exceptionally stable ("aromatic") compound, is known as the Hückel's rule.

Erich Hückel proposes Hückel's rule, which explains when a planar ring molecule will have aromatic properties.

In addition its HOMO is calculated to be a doubly occupied delocalized pi system making it obey Hückel's rule.

This 2(N + 1) rule (with N integer) for spherical aromaticity is the three-dimensional analogue of Hückel's rule.

In organic chemistry, Hückel's rule, also known as the 4n + 2 rule, predicts that a cyclic π-bond system containing a singly even number of p electrons will be aromatic.

The proper use of the symbol is debated; it is used to describe any cyclic pi system in some publications, or only those pi systems that obey Hückel's rule on others.

Previous methods existed, such as the Hückel method which lead to the Hückel's rule, but were limited in their scope, application and complexity, as is the Extended Huckel method.

Furan is aromatic because one of the lone pairs of electrons on the oxygen atom is delocalized into the ring, creating a 4n+2 aromatic system (see Hückel's rule) similar to benzene.

Though it has alternating single and double bonds, it is predicted triplet, unstable and antiaromatic by Hückel's rule, because its ring has 4 π-electrons, and 4 is not twice an odd number.

Hückel's rule was originally based on calculations using the Hückel method, although it can also be justified by considering a particle in a ring system, by the LCAO method and by the Pariser-Parr-Pople method.