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Structural formula of cyclooctadecanonaene
Ball-and-stick model of the cyclooctadecanonaene molecule
3D model (JSmol)
Molar mass 234.34 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cyclooctadecanonaene or [18]annulene is an annulene with chemical formula C
. This hydrocarbon obeys Hückel's rule and is, therefore, an aromatic compound. Theoretical studies show that [18]annulene has only three completely delocalized π bonds associated with its aromaticity, while other six π bonds represent the conjugated 3c-2e π bonds on the periphery of [18]annulene.[1] The compound was first synthesised by Franz Sondheimer.[2]


The original synthesis started by the Eglinton reaction of the di-alkyne 1,5-hexadiyne with copper(II) acetate in pyridine to give the trimer, followed by deprotonation and isomerization with potassium tert-butoxide in tert-butanol and was concluded with hydrogen organic reduction with the Lindlar catalyst.[3] [4]

See also[edit]


  1. ^ Ivanov, A.; Boldyrev. A (2014). "Deciphering aromaticity in porphyrinoids via adaptive natural density partitioning". Org. Biomol. Chem. doi:10.1039/C4OB01018C. 
  2. ^ In the literature and some internet references, Sondheimer is sometimes misspelled as Sandheimer.
  3. ^ Sondheimer, F., Wolovsky, R. and Amiel, Y. (1962). "Unsaturated Macrocyclic Compounds. XXIII. The Synthesis of the Fully Conjugated Macrocyclic Polyenes Cyclooctadecanonaene ([18]Annulene), Cyclotetracosadodecaene ([24]Annulene), and Cyclotriacontapentadecaene ([30]Annulene).". J. Am. Chem. Soc. 68 (2): 274–284. doi:10.1021/ja00861a030. 
  4. ^ K. Stöckel and F. Sondheimer (1988). "[18]Annulene". Org. Synth. ; Coll. Vol., 6, p. 68