3. Aromaticity
Aromaticity is a characteristic in which any planar system in which there is complete
delocalization of pi electron in the ring, and the system contain 4n+2 pi electrons in the ring is
called aromatic.
EXAMPLES:
1.Benzene
2.Naphthalene
3.Anthracene
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4. RULESFOR AROMATICITY
First, it must be cyclic.
Second, every atom in the ring must be conjugated.
Third, the molecule must have [4n+2] pi electrons (Huckels rule)
Fourth, the molecule must be flat/planar (2d structure).
Benzene
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5. HUCKELSRULE
It was discovered by ERICH HUCKEL in 1931.
It states that:
“In order to be aromatic, a molecule must have a certain number of pi electrons (electrons with
pi bonds, or lone pairs within p orbitals) within a closed loop of parallel, adjacent p orbitals.”
4n+2∏ electrons
Where n is any positive integer.
•If n=0 than pie electrons are 2.
•If n=1 than pie electrons are 6.
•Similarly pie electrons would be 2,6,10,14…….
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6. ANTI-AROMATICITY
Anti aromaticity is a characteristic of a cyclic molecule with a π electron system that has higher
energy due to the presence of 4n delocalized (π or lone pair) electrons in it.
4n∏ electrons
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8. REFERENCES
Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)
Prof. Steven Farmer (Sonoma State University)
William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook of Organic Chemistry
bon and Geoff Hutchison from Chemistry StackExchange
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