Cyclononatetraene

Cyclononatetraene is an organic compound with the formula C₉H₁₀. It was first prepared in 1969 by protonation of the corresponding aromatic anion (described below).^[1] It is unstable and isomerizes with a half-life of 50 minutes at room temperature to 3a,7a-dihydro-1H-indene via a thermal 6π disrotatory electrocyclic ring closing.^[2] Upon exposure to ultraviolet light, it undergoes a photochemical 8π electrocyclic ring closing to give bicyclo[6.1.0]nona-2,4,6-triene.^[3]

Cyclononatetraene

Names
IUPAC name Cyclonona-1,3,5,7-tetraene
Identifiers
CAS Number	7129-70-6
3D model (JSmol)	Interactive image
ChemSpider	11341386
PubChem CID	12543719
CompTox Dashboard (EPA)	DTXSID40499530
InChI InChI=1S/C9H10/c1-2-4-6-8-9-7-5-3-1/h1-8H,9H2/b3-1-,4-2-,7-5-,8-6- Key: GORPVKZVZYAFSO-KZPCVFJPSA-N
SMILES C\1/C=C\C=C/C=C\C=C1
Properties
Chemical formula	C9H10
Molar mass	118.179 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Cyclononatetraenyl anion

Cyclononatetraenyl anion is a 10π aromatic system. Two isomers of the cyclononatetraenyl anion are known: the trans,cis,cis,cis isomer ("Pac-Man"-shaped) and the all-cis isomer (a convex enneagon). The former is less stable and isomerizes to the latter upon warming from –40 °C to room temperature.^[4]

The all-cis isomer of C₉H₉⁻ can be prepared by treatment of 9-chlorobicyclo[6.1.0]nona-2,4,6-triene (1) with lithium or potassium metal.^[5] Despite the ring strain resulting from having C–C–C bond angles of 140° instead of the ideal 120° for sp² carbon, this species is believed to be planar and to possess D_9h symmetry. The lithium salt was found to be react with cyclopentadiene to give lithium cyclopentadienide, showing that cyclononatetraene is a weaker acid than cyclopentadiene.^[6]

Cyclononatetraenyl cation

The computed ground-state conformation of C
₉H⁺
₉

Cyclononatetraenyl cation is an 8π system. Its intermediacy is implicated in the solvolysis of 1. The facile solvolysis of 1 suggests that the cation is stabilized. Computation and experimental evidence suggest that C₉H₉⁺ is a rare example of a ground state species that exhibits Möbius aromaticity.^[7][8]

See also

• Cyclopentadiene
• Cyclooctatetraene
• Cycloheptatriene
• Azonine

References

1. Radlick, Phillip; Alford, Gary (November 1969). "Preparation and isolation of cis, cis, cis, cis-1,3,5,7-cyclononatetraene". Journal of the American Chemical Society. 91 (23): 6529–6530. doi:10.1021/ja01051a083. ISSN 0002-7863.^{[permanent dead link‍]}
2. Radlick, Phillip; Gary Alford (1969), "Preparation and isolation of cis, cis, cis, cis-1,3,5,7-cyclononatetraene", Journal of the American Chemical Society, 91 (23): 6529–6530, doi:10.1021/ja01051a083
3. de Meijere, Armin, ed. (2014). Houben-Weyl Methods of Organic Chemistry Vol. E 17b, 4th Edition Supplement: Carbocyclic Three-Membered Ring Compounds, Cyclopropanes: Synthesis. Goettingen: Georg Thieme Verlag. p. 1226. ISBN 978-3131819543.
4. Radlick, Phillip; Gary Alford (1969), "trans,cis,cis,cis-Cyclononatetraenyl Anion, a New Aromatic 10 π System", Angewandte Chemie International Edition in English, 8 (12): 984, doi:10.1002/anie.196909841
5. Fray, G. I. (1978). The chemistry of cyclo-octatetraene and its derivatives. Saxton, Roy Gerald, 1945-. Cambridge: Cambridge University Press. ISBN 0521215803. OCLC 3033135.
6. Cram, Donald J. (1965). Fundamentals of Carbanion Chemistry. Burlington: Elsevier Science. ISBN 9780323162449. OCLC 843200178.
7. Thermal bicyclo[6.1.0]nonatrienyl chloride-dihydroindenyl chloride rearrangement Paul v. R. Schleyer, James C. Barborak, Tah Mun Su, Gernot Boche, and G. Schneider J. Am. Chem. Soc.; 1971; 93(1) pp 279 - 281; doi:10.1021/ja00730a063
8. Topology in Chemistry: Designing Möbius Molecules Herges, R. Chem. Rev.; (Review); 2006; 106(12); 4820-4842.doi:10.1021/cr0505425