Fulvalene

Fulvalene (bicyclopentadienylidene) is the member of the fulvalene family with the molecular formula C₁₀H₈. It is of theoretical interest as one of the simplest non-benzenoid conjugated hydrocarbons. Fulvalene is an unstable isomer of the more common benzenoid aromatic compounds naphthalene and azulene. Fulvalene consists of two 5-membered rings, each with two double bonds, joined by yet a fifth double bond. It has D_2h symmetry.

Fulvalene

Names
Preferred IUPAC name [1,1′-Bi(cyclopentylidene)]-2,2′,4,4′-tetraene
Other names Bicyclopentyliden-2,4,2′,4′-tetraene 1,1′-Bi[cyclopentadienylidene] Pentafulvalene Bicyclopentadienylidene [5,5′]Bicyclopentadienylidene
Identifiers
CAS Number	91-12-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:51994 Y
ChemSpider	9083553 Y
PubChem CID	10908294
UNII	V2K3QQS6YW Y
CompTox Dashboard (EPA)	DTXSID10447902
InChI InChI=1S/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H Y Key: XEOSBIMHSUFHQH-UHFFFAOYSA-N Y InChI=1/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H Key: XEOSBIMHSUFHQH-UHFFFAOYAP
SMILES C=1\C=C/C(/C=1)=C2\C=C/C=C2
Properties
Chemical formula	C10H8
Molar mass	128.174 g·mol−1
Density	1.129 g/ml
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

History

Biferrocene and bis(fulvalene)diiron (not shown) are complexes of the fulvalene dianion.

An earlier attempt at synthesis of fulvalene in 1951 by Pauson and Kealy resulted in the accidental discovery of ferrocene.^[1] Its synthesis was first reported in 1958 by E. A. Matzner, working under William von Eggers Doering.^[2] In this method, the cyclopentadienyl anion is coupled with iodine to the dihydrofulvalene. Double deprotonation of the dihydrofulvalene with n-butyllithium gives the dilithio derivative, which is oxidized by oxygen. Fulvalene was spectroscopically observed at −196 °C (77 K) from photolysis of diazocyclopentadiene, which induces dimerization of cyclopentadiene-derived carbenes.^[3] The compound was isolated in 1986^[4] and was found to be nonaromatic. Above −50 °C (223 K) it dimerizes by a Diels–Alder reaction.

Derivatives

Perchlorofulvalene (C₄Cl₄C)₂ is quite stable in contrast to fulvalene itself.^[5]

See also

• Fulvenes, (CH=CH)₂C=CH₂ and substituted derivatives
• Tetrathiafulvalene, C₂H₂S₂C=CS₂C₂H₂