Aromaticity: Huckel’s Rule, 3-membered Cyclic Species, 5-membered Cyclic Species | Organic Chemistry

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Topic

Aromaticity
Learning Outcomes
After studying this lesson, you shall be able to:
Aromaticity
Huckel’s Rule and aromaticity
Three membered cyclic species
Five membered cyclic species
Aromaticity
The aromatic compounds apparently contain alternate double and single bonds in a cyclic structure and resemble benzene in chemical behaviour.
They undergo substitution rather than addition reactions. This characteristic behaviour is known aromaticity.
These compounds exhibit significantly high diamagnetic susceptibility.
Cyclic electron delocalization also results in bond length equalization, abnormal chemical shifts and magnetic anisotropies.

1. Chemical behavior: electrophilic aromatic substitution.
2. Structure: bond length equalization due to cyclic delocalization.
3. Energetic: enhanced stability (large resonance energy).
4. Magnetic: "ring current" effects.
a) anomalous chemical shifts in NMR.
b) large magnetic anisotropies
c) high diamagnetic susceptibility