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Hückel's rule is not valid for many compounds containing more than one ring. For example, pyrene and trans-bicalicene contain 16 conjugated electrons (8 bonds), and coronene contains 24 conjugated electrons (12 bonds). Both of these polycyclic molecules are aromatic, even though they fail the 4n + 2 rule. Indeed, Hückel's rule can only be ...
In fact, all cyclic conjugated hydrocarbons with a total of 4n π-electrons share this molecular orbital pattern, and this forms the basis of Hückel's rule. Dewar reactivity numbers deriving from the Hückel approach correctly predict the reactivity of aromatic systems with nucleophiles and electrophiles .
It is seen that with one MO at the bottom and then groups of degenerate pairs, the Hückel systems will accommodate 4n + 2 electrons, following the ordinary Hückel rule. However, in contrast, the Möbius Systems have degenerate pairs of molecular orbitals starting at the circle bottom and thus will accommodate 4 n electrons.
The famous Hückel 4n+2 rule for determining whether ring molecules composed of C=C bonds would show aromatic properties was first stated clearly by Doering in a 1951 article on tropolone. [6] Tropolone had been recognised as an aromatic molecule by Dewar in 1945. In 1936, Hückel developed the theory of π-conjugated biradicals (non-Kekulé ...
Hückel or Huckel may refer to: Erich Hückel (1896-1980), German physicist and chemist Debye–Hückel equation (named after Peter Debye and Erich Hückel), in chemistry, a method of calculating activity coefficients; Hückel method (named after Erich Hückel), a method for the determination of energies of molecular orbitals
The method was first used by Roald Hoffmann who developed, with Robert Burns Woodward, rules for elucidating reaction mechanisms (the Woodward–Hoffmann rules). He used pictures of the molecular orbitals from extended Hückel theory to work out the orbital interactions in these cycloaddition reactions.
Unlike aromatic compounds, which follow Hückel's rule ([4n+2] π electrons) [1] and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions.
I noticed that the orbital angular momentum quantum number, ℓ has a rule that says any sub-shell can hold a maximum of 4ℓ + 2 electrons. Since 4ℓ + 2 looks quite similar to the 4n + 2 electrons of Hückel's rule, I figure they might be correlated to each other and thus both pages might benefit from this being added.