Prismane

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Prismane
Chemical structure of prismaneChemical structure of prismane
CPK model of prismane
Systematic name Tetracyclo[2.2.0.02,6.03,5]hexane
Chemical formula C6H6
Molecular mass 78.1134 g/mol
Density  ? g/cm3
Melting point  ? °C
Boiling point  ? °C
CAS number [650-42-0]
SMILES C12C3C1C4C2C34
Disclaimer and references

Prismane is a polycyclic hydrocarbon of the chemical formula C6H6. It is an isomer of benzene, but it is far less stable than benzene is. The carbon atoms of the prismane molecule are arranged in the shape of a six-atom triangular prism. The systematic name is tetracyclo[2.2.0.02,6.03,5]hexane. Albert Ladenburg proposed this structure for the compound now known as benzene.[1] The compound was not synthesized in the laboratory until 1973.[2]

Contents

[edit] History

The discussion about the structure of benzene in the mid 18th century yielded several structures to the formula C6H6, which was accesable by Combustion analysis. The first of Kekulé in 1867, which later proofed to be the right one. This structure inspired several others to come up with concurring structures, like Ladenburg with the prismane, Dewar with the dewar benzene, Koerner and Claus with the claus benzene. Some of these structures could be synthesized in the following years. As an isomere of benzene, like the other announced structures, and because it is part of the struggle understanding mesomeric structures and resonance of benzene, prismane is still a often cited molecule. Some computational chemists still research the differences in the possible isomeres of C6H6. [3]

[edit] Properties

The deviation of the carbon carbon bond angle from 109° with in a tetrahedron to the 60° in a triangle, leads to a high ring strain, similar to that of cyclopropane. Due to the this ring strain, the bonds have a low bond energy and break at a low activation energy, which makes synthesis of the molecule difficult. The molecule in which all the six hydrogens are substituted by methyl groups (hexamethylprismane) has a higer stability and was synthesiced by rearrangement reactions in 1966.[4]

[edit] Synthesis

Synthesis of Prismane

The synthesis starts from benzvalene (1) and the 4-phenyltriazolidone which is a strong dienophile. The reaction is a step wise Diels-Alder like reaction forming a carbocation as intermediate. The aduct (2) is than hydrolysed under basic conditions and afterwards transformed into a copper(II) chloride derivate with acidic copper(II) chloride. neurtalzed with a strong base the azo compound (3) could be crystallized with 65% yield. Last step is a photolysis of the azo compound. This photolysis leads to a biradical which forms the prismane (4) and nitrogen with a yield of less than 10%.

[edit] Analytical Data

[edit] 1H-NMR

1H-NMR (CCl4): δ = 7.72 ppm

[edit] 13C-NMR

13C-NMR(C6D6): δ = 30.6 ppm

[edit] Mass-spectroscopy

EI-MS (70 eV): m/z (%) = 78 (100) [M+], 77 (20) [M+ - H], 52 (22), 39 (13).

[edit] References

  1. ^ Ladenburg A. (1869). ".". Chemische Berichte 2: 140.
  2. ^ Katz T. J., Acton N. (1973). "Synthesis of Prismane". Journal of the American Chemical Society 95: 2738-2739. DOI:10.1021/ja00789a084.
  3. ^ UD Priyakumar, TC Dinadayalane, GN Sastry (2002). "A computational study of the valence isomers of benzene and their group V hetero analogs". New J. Chem. 26: 347-353.
  4. ^ Lemal D. M., Lokensgard J. P. (1966). "Hexamethylprismane". Journal of the American Chemical Society 88: pp 5934 - 5935. DOI:10.1021/ja00976a046.

[edit] See also

[edit] External links


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