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Ju Long

What is non-hückel double bond of Aromaticity? [duplicate]

Cramer Beasly  Follow

In the given molecule Pyrene , the π bond shown in green is in cross conjugation (shown in green in figure 1). This bond( figure 2) is excluded from interaction with rest of conjugated system. Hence , the central $\ce{C=C}$ isn't hosted by the largest p orbital loop, so it's not counted towards Hückel's rule for aromaticity.

The outer periphery (shown in blue in figure 3), is a loop of $\ce{14 π}$ electrons , therefore aromatic. This may be possible hückel double bond you are referring to.

The π bond in cross-conjugation (shown in green) maybe non-hückel double bond.

Pyrene structure

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Jim Grupé  Follow
Beware: The central pi bond does not count towards the Hückel rule, however that does NOT mean that bond is not part of the aromatic system!More
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