Annulenes
[14]-Annulenes
- Compound A, is aromatic in spite of interactions of the inner hydrogens, which do not permit coplanarity, the molecule is diatropic.
- The inner hydrogens have a chemical shift of 0.00 ppm and the outer hydrogens 7.6 ppm.
- The molecule disintegrates on exposure to air and light.
- A number of stable bridged [14]-annulenes are known, B is an example.
- Compound A, is aromatic in spite of interactions of the inner hydrogens, which do not permit coplanarity, the molecule is diatropic.
- The inner hydrogens have a chemical shift of 0.00 ppm and the outer hydrogens 7.6 ppm.
- The molecule disintegrates on exposure to air and light.
- A number of stable bridged [14]-annulenes are known, B is an example.
[18]-annulene (Cyclo-octadecanonaene)
This type are Huckel systems and the ones that are planar should be aromatic.
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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