Overview

annulenes


'annulenes' can also refer to...

 

More Like This

Show all results sharing this subject:

  • Chemistry

GO

Show Summary Details

Quick Reference

Organic hydrocarbons that have molecules containing simple single rings of carbon atoms linked by alternating single and double bonds. Such compounds have even numbers of carbon atoms. Cyclo-octatetraene, C8H8, is the next in the series following benzene. Higher annulenes are usually referred to by the number of carbon atoms in the ring, as in [10]-annulene, C10H10, [12]-annulene, C12H12, etc. The lower members are not stable as a result of the interactions between hydrogen atoms inside the ring. This is true even for molecules that have the necessary number of pi electrons to be aromatic compounds. Thus, [10]-annulene has 4n+2 pi electrons with n=2, but is not aromatic because it is not planar. [14]-annulene also has a suitable number of pi electrons to be aromatic (n=3) but is not planar because of interaction between the inner hydrogens.

The compound [18]-annulene is large enough to be planar and obeys the Hückel rule (4n+2=18, with n=4). It is a brownish red fairly stable reactive solid. NMR evidence shows that it has aromatic character. The annulene with n=7, [30]-annulene, can also exist in a planar form but is highly unstable. See also pseudoaromatic.

Annulenes

Subjects: Chemistry.


Reference entries

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.