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