Bullvalene

Bullvalene is a C₁₀H₁₀ hydrocarbon with a unique property: It is a fluxional molecule in which all of the bonds rapidly form and break so that all of the carbon and hydrogen atoms are equivalent on the NMR timescale. At ambient temperature, its ¹H and ¹³C NMR spectra consist of broad humps, which coalesce into sharp singlets at temperatures ≈30–50 °C above its melting point. At low temperature, all of the atoms are distinguishable.

Fluxional molecules are different from aromatic molecules, which are sometimes drawn with alternating single and double bonds. That notation is misleading, because aromatics contain continuous π bonds that cannot be distinguished as single or double on any timescale.

Bullvalene was first synthesized and characterized in 1963 by Gerhard Schröder¹ at Union Carbide European Research Associates (Brussels). Schröder synthesized the compound via the photolysis of the dimer of cyclooctatetraene² with the expulsion of one molecule of benzene. Four years later, William von Eggers Doering and co-workers at Yale University (New Haven, CT) described what they termed a “rational” seven-step synthesis of bullvalene beginning from 1,3,5-cycloheptatriene-7-carboxylic acid³.

Because bullvalene is a laboratory curiosity, no credible hazard information about it exists; but it should have a moderate hazard profile similar to those of other unsaturated cyclic C₁₀ hydrocarbons such as dicyclopentadiene⁴.

Where did the name “bullvalene” come from? Two stories exist: In one, a skeptical graduate student thought that the proposed molecule could not be made and described the concept as “bull—“. In the other, the name could have come from Doering’s nickname “Bull”.

For further information about bullvalene, see the 2001 article “The Bullvalene Story” by Addison Ault at Cornell College (Mount Vernon, IA).

1. Not to be confused with the former German chancellor of the same name.
2. CAS Reg. No. 629-20-9.
3. CAS Reg. No. 4440-40-8.
4. CAS Reg. No. 77-73-6.