This document defines aromaticity and its key rules. Aromatic molecules have complete delocalization of pi electrons in a planar, conjugated ring system containing 4n+2 pi electrons, as defined by Huckel's rule. Examples of aromatic molecules include benzene and naphthalene. Anti-aromatic molecules have higher energy and contain a 4n pi electron system that is not fully delocalized.

1. STRUCTUREAROMATICITY
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2. CONTENTS
Aromaticity
Rules for aromaticity
Huckels rule
Anti aromaticity
Example
References
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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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7. EXAMPLES
Planar
4n+2 pie electrons i.e. 10 electrons
Conjugated
Ring
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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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