Benzvalene

Benzvalene

Benzvalene

Chemical compound

Benzvalene is an organic compound and one of several isomers of benzene.[1] It was first synthesized in 1967 by K. E. Wilzbach et al. [2] via photolysis of benzene and the synthesis was later improved by Thomas J. Katz et al.[3][4]

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The 1971 synthesis consisted of treating cyclopentadiene with methyllithium in dimethyl ether and then with dichloromethane and methyllithium in diethyl ether at −45 °C. It can also be formed in low yield (along with fulvene and Dewar benzene) by irradiation of benzene at 237 to 254 nm.[5] The hydrocarbon in solution was described as having an extremely foul odor. Due to the high steric strain present in benzvalene, the pure compound (~71 kcal/mol higher in energy than benzene) easily detonates, for example by scratching.

The compound converts to benzene with a chemical half-life of approximately 10 days. This symmetry-forbidden transition is believed to take place through a diradical intermediate.[6]

Polybenzvalene

Benzvalene can be polymerized in a ROMP process to polybenzvalene.[7] This polymer contains highly strained bicyclobutane rings which again makes it a sensitive material. The rings can be isomerized to 1,3-dienes and for this reason polybenzvalene has been investigated as a precursor to polyacetylene.

References

  1. [1]
    Christl, M. (1981). "Benzvalene—Properties and Synthetic Potential". Angewandte Chemie International Edition in English. 20 (67): 529–546. doi:10.1002/anie.198105291.
  2. [2]
    Wilzbach, K. E.; Ritscher, J. S.; Kaplan, L. (1967). "Benzvalene, the Tricyclic Valence Isomer of Benzene". Journal of the American Chemical Society. 89 (4): 1031. doi:10.1021/ja00980a053.
  3. [3]
    Katz, T. J.; Wang, E. J.; Acton, N. (1971). "Benzvalene synthesis". Journal of the American Chemical Society. 93 (15): 3782. doi:10.1021/ja00744a045.
  4. [4]
    Katz, T. J.; Roth, R. J.; Acton, N.; Carnahan, E. J. (1999). "Synthesis of Benzvalene". The Journal of Organic Chemistry. 64 (20): 7663. doi:10.1021/jo990883g.
  5. [5]
    Kaplan, Louis; Wilzbach, K. E. (1968-06-01). "Photolysis of benzene vapor. Benzvalene formation at wavelengths 2537-2370 A". Journal of the American Chemical Society. 90 (12): 3291–3292. doi:10.1021/ja01014a086. ISSN 0002-7863.
  6. [6]
    Scott, Lawrence T.; Jones, Maitland. (1972). "Rearrangements and interconversions of compounds of the formula (CH)n". Chemical Reviews. 72 (2): 181. doi:10.1021/cr60276a004.
  7. [7]
    Swager, T. M.; Dougherty, D. A.; Grubbs, R. H. (1988). "Strained rings as a source of unsaturation: polybenzvalene, a new soluble polyacetylene precursor". Journal of the American Chemical Society. 110 (9): 2973. doi:10.1021/ja00217a049.

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