Hückel rule
Quick Summary
The Hückel rule, developed by physicist Erich Hückel, is a principle in organic chemistry used to determine if a planar, monocyclic, conjugated system of double bonds is aromatic.1
The rule states that such compounds are aromatic if they contain 4n + 2 pi electrons, where n is a whole number (0, 1, 2, etc.). This means compounds with 2, 6, 10, 14, and so on, pi electrons are considered aromatic. Benzene, with 6 pi electrons, is a prime example of an aromatic compound that follows this rule. Conversely, compounds with 4, 8, 12, or 16 pi electrons are not aromatic.12
Aromatic compounds exhibit special stability due to the delocalization of these pi electrons within the ring system. This stability is reflected in their lower reactivity compared to non-aromatic compounds, often reacting through substitution rather than addition.2
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