Question

How do you count pi electrons in aromatic compounds?

Answer 1

Aromatic compounds:

1. Compounds must meet all four characteristics to be classified as aromatic or contain aromaticity. The molecule must be cyclic. Benzene is an example.
2. In a cyclic ring, each atom must be conjugated. As a result, the cyclic ring delocalized pi-electron system will disperse more easily. As a result, each atom in the cyclic ring must have an empty $\mathrm{p}$ orbital and be capable of resonance.
3. All aromatic compounds must always follow Huckel's Rule, which states that the total number of pi electrons in the molecule can be calculated using the formula ($4n+2$), where ‘n’ can be any positive integer (including zero).
4. To be classified as an aromatic molecule, the molecule must be planar or flat.

Huckel's Rule:

1. According to Huckel's Rule, if a cyclic, planar molecule possesses $4n+2$ pi Electrons, then it is Aromatic.
2. It is used to determine pi electrons in a compound.

Example:

• The given benzene structure shows it has $6$ pi electrons, and it satisfies the huckel's rule as n, in this case, is 1 and the number of electrons$=4\times 1+2\Rightarrow 6$. Hence it is aromatic.
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• Whereas in cyclobutadiene, it has $4$ pi-electron and it does not satisfy huckel's rule (if $n=0$ we get $2$ pi electrons and if $n=1$ we get $6$ pi electrons). Therefore, it is non-aromatic.
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