Prismane

Chembox new
Name = Prismane
ImageFile = Prisman2.svg
ImageName = Chemical structure of prismane
ImageFile1 = prismane-stick.png ImageName1 = Chemical structure of prismane
ImageFile2 = prismane-CPK.png ImageName2 = CPK model of prismane
IUPACName = Tetracyclo [2.2.0.0^2,6.0^3,5] hexane
Section1 = Chembox Identifiers
CASNo = 650-42-0
SMILES = C12C3C1C4C2C34
Section2 = Chembox Properties
Formula = carbon|6hydrogen|6
MolarMass = 78.1134 g/mol
Density = ? g/cm³
MeltingPt =
BoilingPt = °C

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 [2.2.0.0^2,6.0^3,5] hexane. Albert Ladenburg proposed this structure for the compound now known as benzene. [cite journal | author= Ladenburg A.|title=.| journal= Chemische Berichte| volume= 2| pages= 140 | year=1869] The compound was not synthesized in the laboratory until 1973. [cite journal | author=Katz T. J., Acton N. | title= Synthesis of Prismane | journal= Journal of the American Chemical Society | year=1973 | volume=95 | pages=2738–2739|doi =10.1021/ja00789a084 ]

History

The discussion about the structure of benzene in the mid 19th 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. [cite journal | author=UD Priyakumar, TC Dinadayalane, GN Sastry
title=A computational study of the valence isomers of benzene and their group V hetero analogs
journal= New J. Chem.| volume= 26| pages= 347–353 | year=2002|url =http://pubs.rsc.org/ej/NJ/2002/b109067d.pdf
doi=10.1039/b109067d ]

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. [cite journal | author= Lemal D. M., Lokensgard J. P.| title= Hexamethylprismane | journal= Journal of the American Chemical Society | year=1966 | volume=88 | pages=pp 5934–5935|doi =10.1021/ja00976a046 ]

ynthesis

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

ee also

* Prismane C8, C₈
* Cubane, C₈H₈
* Fullerene

External links

* [http://www.chm.bris.ac.uk/sillymolecules/sillymols.htm Molecules with silly or unusual Names]