Bicyclopropenyl (bicycloprop-2-enyl, C₆H₆) is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

and one of several

valence isomer In organic chemistry, two molecules are valence isomers when they are constitutional isomers that can interconvert through pericyclic reactions. Benzene There are many valence isomers one can draw for the C6H6 formula benzene. Some were original ...

s of

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

. The molecule can be described as two coupled

cyclopropene Cyclopropene is an organic compound with the formula . It is the simplest cycloalkene. Because the ring is highly strained, cyclopropene is difficult to prepare and highly reactive. This colorless gas has been the subject for many fundamental s ...

units. The positions of the

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

groups can vary and therefore two other isomers are known: bicycloprop-1,2-enyl and bicyclopropen-1-yl. : Bicyclopropenyl

The synthesis of all three isomers was reported in 1989 By Billups and Haley. The 3,3 isomer was formed in two steps by reaction of ''1,4-bis(trimethylsilyl)buta-1,3-diene'' with

methyllithium Methyllithium is the simplest organolithium reagent, with the empirical formula LiCH3. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used i ...

and

dichloromethane Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with ...

, introducing two cyclopropane rings into the molecule. The bis(2-chloro-3-(trimethylsilyl)cyclopropan-1-yl) formed is reacted with

TBAF Tetra-''n''-butylammonium fluoride, commonly abbreviated to TBAF and ''n''-Bu4NF, is a quaternary ammonium salt with the chemical formula (CH3CH2CH2CH2)4N+F−. It is commercially available as the white solid trihydrate and as a solution in tetra ...

. In this latter reaction fluoride couples to the trimethylsilyl group, in the process forming the double bond and forcing the chlorine atom to leave as chloride. In presence of

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

ions bicycloprop-2-enyl rearranges to

Dewar benzene Dewar benzene (also spelled ''dewarbenzene'') or bicyclo .2.0exa-2,5-diene is a bicyclic isomer of benzene with the molecular formula C6H6. The compound is named after James Dewar who included this structure in a list of possible C6H6 structures i ...

. The compound can also be trapped by

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−. This colorless liquid has a strong and unpleasant odor. At room temperature, ...

. Above -10 °C it decomposes with

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

. An X-ray crystal structure has been reported. The

bond length In molecular geometry, bond length or bond distance is defined as the average distance between Atomic nucleus, nuclei of two chemical bond, bonded atoms in a molecule. It is a Transferability (chemistry), transferable property of a bond between at ...

for the central bond is short by 1.503

Ångström The angstrom (; ) is a unit of length equal to m; that is, one ten-billionth of a metre, a hundred-millionth of a centimetre, 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–18 ...

(150.3 pm). The other two isomers are increasingly unstable. Bicycloprop-1-enyl can only be detected in trapping experiments. Derivatives can be much more stable, for example perfluorohexamethylbicyclopropenyl that must be heated to 360 °C to be as unstable.

References

{{Reflist Bicyclic compounds Cyclopropenes