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Annulenes - 14 electron System , 14 Annulenes

[18]-annulene (Cyclo-octadecanonaene)

This type are Huckel systems and the ones that are planar should be aromatic.

Annulenes - 18 electron system , 18 Annulenes

The six inner hydrogens have some steric hindrance, but not sufficient to make the molecule appreciably non-coplanar. It is therefore aromatic.

It undergoes nitration bromination and acetylation. It has resonance energy of about 37 kcal/mole.

The NMR spectrum indicates the molecule to be diatropic.

The twelve outer protons have a chemical shift of 9.0 ppm and the six inner protons, which are highly shielded, have a value of 3.0 ppm.

It is a stable crystalline solid but decomposes in solution at room temperature.

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