fulvalene
{{Chembox
| Watchedfields = changed
| verifiedrevid = 443829133
| PIN = [1,1′-Bi(cyclopentylidene)]-2,2′,4,4′-tetraene
| OtherNames = Bicyclopentyliden-2,4,2′,4′-tetraene
1,1′-Bi[cyclopentadienylidene]
Pentafulvalene
Bicyclopentadienylidene
[5,5′]Bicyclopentadienylidene
| ImageFile1 = Fulvalen.png
| ImageSize1 = 180
| ImageAlt1 = Skeletal formula
| ImageFile2 = Pentafulvalene-3D-spacefill.png
| ImageSize2 = 180
| ImageAlt2 = Space-filling model
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 9083553
| PubChem = 10908294
| InChI = 1/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H
| InChIKey = XEOSBIMHSUFHQH-UHFFFAOYAP
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 51994
| SMILES = C=1\C=C/C(/C=1)=C2\C=C/C=C2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C10H8/c1-2-6-9(5-1)10-7-3-4-8-10/h1-8H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = XEOSBIMHSUFHQH-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 91-12-3
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = V2K3QQS6YW
}}
| Section2 = {{Chembox Properties
| C = 10 | H = 8
| Density=1.129 g/ml
}}
}}
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 D2h symmetry.
History
File:Biferrocene.svg 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.{{cite journal
| author = T. J. Kealy, P. L. Pauson
| title = A New Type of Organo-Iron Compound
| journal = Nature
| year = 1951
| volume = 168
| pages = 1039–1040
| doi = 10.1038/1681039b0
| issue=4285| bibcode = 1951Natur.168.1039K
| s2cid = 4181383
}} Its synthesis was first reported in 1958 by E. A. Matzner, working under William von Eggers Doering.Dissertation Abstracts Int'l 26-06 page 3270 6411876. 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 {{convert|77|K|C|0|order=flip}} from photolysis of diazocyclopentadiene, which induces dimerization of cyclopentadiene-derived carbenes.{{cite journal|doi=10.1021/ja01531a008|title=Photochemical Experiments in Rigid Media at Low Temperatures. II. The Reactions of Methylene, Cyclopentadienylene and Diphenylmethylene|year=1959|last1=Demore|first1=William B.|last2=Pritchard|first2=H. O.|last3=Davidson|first3=Norman|journal=Journal of the American Chemical Society|volume=81|issue=22|pages=5874–5879}} The compound was isolated in 1986{{cite journal|title=Synthese von Pentafulvalen durch oxidative Kupplung von Cyclopentadienid mittels Kupfer(II)-chlorid|first1=André|last1=Escher|first2=Werner|last2=Rutsch|first3=Markus|last3=Neuenschwander|journal=Helvetica Chimica Acta|volume=69|page=1644–1654|year=1986|issue=7|doi=10.1002/hlca.19860690719}} and was found to be nonaromatic. Above {{convert|−50|C|K|0}} it dimerizes by a Diels–Alder reaction.
Derivatives
Perchlorofulvalene (C4Cl4C)2 is quite stable in contrast to fulvalene itself.{{cite journal |author=Mark, V. |doi=10.15227/orgsyn.046.0093|title=Perchlorofulvalene|journal=Organic Syntheses|year=1966|volume=46|page=93}}
See also
- Fulvenes, (CH=CH)2C=CH2 and substituted derivatives
- Tetrathiafulvalene, C2H2S2C=CS2C2H2