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| Names | |
|---|---|
| Preferred IUPAC name [1,1′-Bi(cyclopropane)]-1,1′-diene | |
| Other names 1,1′-Bi(cycloprop-2-en-1-yl) 3,3'-Bicyclopropenyl | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| Properties | |
| C6H6 | |
| Molar mass | 78.1 g/mol |
| Melting point | −75 °C; −103 °F; 198 K |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Bicyclopropenyl (bicycloprop-2-enyl, C6H6) is anorganic compound and one of severalvalence isomers ofbenzene. The molecule can be described as two coupledcyclopropene units. The positions of thealkene groups can vary and therefore two other isomers are known: bicycloprop-1,2-enyl and bicyclopropen-1-yl.
The synthesis of all three isomers was reported in 1989 By Billups and Haley.[1][2] The 3,3 isomer was formed in two steps by reaction of1,4-bis(trimethylsilyl)buta-1,3-diene withmethyllithium anddichloromethane, introducing two cyclopropane rings into the molecule. The bis(2-chloro-3-(trimethylsilyl)cyclopropan-1-yl) formed is reacted withTBAF. 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 ofsilver ions bicycloprop-2-enyl rearranges toDewar benzene. The compound can also be trapped bycyclopentadiene. Above −10 °C it decomposes withpolymerization.
AnX-ray crystal structure has been reported.[3] Thebond length for the central bond is short by 1.503Ångström (150.3 pm).
The other two isomers are increasingly unstable. Bicycloprop-1-enyl can only be detected in trapping experiments.
| Properties benzene valence isomers | ||
|---|---|---|
| Compound | Calc.Heat of formation[4][5] | Calc. Heat of formation[4][5] |
| 0 K (KJ/mole) | 298 K (KJ/mole) | |
| Benzene | 100.5 | 82.0 |
| Dewar benzene | 415.5 | 397.1 |
| Benzvalene | 397.5 | 378.1 |
| Prismane | 567.2 | 547.0 |
| Bicycloprop-2-enyl | 593.6 | 578.8 |
Derivatives can be much more stable, for example perfluorohexamethylbicyclopropenyl that must be heated to 360 °C to be as unstable.[6]
