Fulvalene

{{Chembox | Watchedfields = changed | verifiedrevid = 443829133 | PIN = [1,1′-Bi(cyclopentylidene)]-2,2′,4,4′-tetraene | OtherNames = Bicyclopentyliden-2,4,2′,4′-tetraene <br /> 1,1′-Bi[cyclopentadienylidene] <br /> Pentafulvalene <br /> Bicyclopentadienylidene <br /> [5,5′]Bicyclopentadienylidene | ImageFile1 = Fulvalene.svg | 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 D_2h symmetry.

== History == [[File:Biferrocene.svg|thumb|left|132 px|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.<ref>{{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 }}</ref> Its synthesis was first reported in 1958 by E. A. Matzner, working under William von Eggers Doering.<ref>''Dissertation Abstracts Int'l'' 26-06 page 3270 6411876.</ref> 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.<ref>{{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}}</ref> The compound was isolated in 1986<ref>{{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}}</ref> 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.<ref>{{cite journal |author=Mark, V. |doi=10.15227/orgsyn.046.0093|title=Perchlorofulvalene|journal=Organic Syntheses|year=1966|volume=46|page=93}}</ref>

==See also== * Fulvenes, (CH=CH)₂C=CH₂ and substituted derivatives * Tetrathiafulvalene, C₂H₂S₂C=CS₂C₂H₂ * Tetramethyltetraselenafulvalene, {{chem2|C10H12Se4}}

==References== {{Reflist}}

Category:Hydrocarbons Category:Fulvalenes