Bicyclopropenyl

Bicyclopropenyl
Names
IUPAC name
Bicycloprop-2-enyl
Other names
3,3'-bicyclopropenyl
Identifiers
62595-44-2 N
ChemSpider 126965 N
Jmol interactive 3D Image
PubChem 143919
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 their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Bicyclopropenyl (bicycloprop-2-enyl, C6H6) is an organic compound and one of several valence isomers of benzene. The molecule can be described as two coupled cyclopropene units. The positions of the alkene 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 of 1,4-bis(trimethylsilyl)buta-1,3-diene with methyllithium and dichloromethane, introducing two cyclopropane rings into the molecule. The bis(2-chloro-3-(trimethylsilyl)cyclopropan-1-yl) formed is reacted with TBAF. 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 ions bicycloprop-2-enyl rearranges to Dewar benzene. The compound can also be trapped by cyclopentadiene. Above -10 °C it decomposes with polymerization.

An X-ray crystal structure has been reported.[3] The bond length for the central bond is short by 1.503 Ångström (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

References

  1. Billups, W. E.; Haley, M. M. (1989). "Bicycloprop-2-enyl (C6H6)". Angewandte Chemie International Edition in English 28 (12): 1711. doi:10.1002/anie.198917111.
  2. Billups, W.; m. Haley, M.; Boese, R.; Bläser, D. (1994). "Synthesis of the bicyclopropenyls". Tetrahedron 50 (36): 10693–10700. doi:10.1016/S0040-4020(01)89261-9.
  3. Boese, R.; Blaeser, D.; Gleiter, R.; Pfeifer, K. H.; Billups, W. E.; Haley, M. M. (1993). "Structure and photoelectron spectrum of 3,3'-bicyclopropenyl". Journal of the American Chemical Society 115 (2): 743. doi:10.1021/ja00055a052.
  4. 1 2 Cheung, Y. (1998). "Ab initio calculations of the heats of formation for (CH)6 isomers". Journal of Molecular Structure: THEOCHEM 454: 17–20. doi:10.1016/S0166-1280(98)00189-4.
  5. 1 2 G2 level, isodesmic bond separation scheme
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