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Prismane



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 with the chemical formula C6H6. It is an isomer of benzene, but it is far less stable than benzene. 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]

Additional recommended knowledge

Contents

History

The discussion about the structure of benzene in the mid 18th century yielded several structures for the formula C6H6, which was accessible by combustion analysis. The first, proposed by Kekulé in 1867, later proved to be the right one. This structure inspired several others to come up with concurring structures; for example, Ladenburg with prismane, Dewar with Dewar benzene, and Koerner and Claus with claus benzene. Some of these structures could be synthesized in the following years. Prismane, like the other proposed structures for benzene, is still often cited in the literature, because it is part of the historical struggle toward understanding the mesomeric structures and resonance of benzene. Some computational chemists still research the differences among the possible isomers of C6H6.[3]

Properties

The deviation of the carbon-carbon bond angle from 109° in a tetrahedron to 60° in a triangle leads to a high ring strain, similar to that of cyclopropane. Due to 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 six hydrogens are substituted by methyl groups (hexamethylprismane) has a higher stability and was synthesized by rearrangement reactions in 1966.[4]

Synthesis


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


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.

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Prismane". A list of authors is available in Wikipedia.
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