Prismane

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Prismane
Chemical structure of prismane
Chemical structure of prismane
Chemical structure of prismane
Chemical structure of prismane
CPK model of prismane
Names
Preferred IUPAC name
Tetracyclo[2.2.0.02,6.03,5]hexane[1]
Identifiers
3D model (
JSmol
)
ChemSpider
  • InChI=1S/C6H6/c1-2-3(1)6-4(1)5(2)6/h1-6H checkY
    Key: RCJOMOPNGOSMJU-UHFFFAOYSA-N checkY
  • InChI=1/C6H6/c1-2-3(1)6-4(1)5(2)6/h1-6H
    Key: RCJOMOPNGOSMJU-UHFFFAOYAA
  • C12C3C1C4C2C34
Properties
C6H6
Molar mass 78.114 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Prismane or 'Ladenburg benzene' is a

triangular prism—this compound is the parent and simplest member of the prismanes class of molecules. Albert Ladenburg proposed this structure for the compound now known as benzene.[2] The compound was not synthesized until 1973.[3]

History

In the mid 19th century, investigators proposed several possible structures for benzene which were consistent with its empirical formula, C6H6, which had been determined by

Kekulé in 1865, later proved to be closest to the true structure of benzene. This structure inspired several others to draw structures that were consistent with benzene's empirical formula; for example, Ladenburg proposed prismane, Dewar proposed Dewar benzene, and Koerner and Claus proposed Claus' benzene. Some of these structures would 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 between the possible isomers of C6H6.[4]

Properties

Prismane is a colourless liquid at room temperature. The deviation of the carbon-carbon bond angle from 109° to 60° in a triangle leads to a high ring strain, reminiscent of that of cyclopropane but greater. The compound is explosive, which is unusual for a hydrocarbon. 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; Woodward and Hoffmann noted that prismane's thermal rearrangement to benzene is symmetry-forbidden, comparing it to "an angry tiger unable to break out of a paper cage." On account of its strain energy and the aromatic stabilization of benzene, the molecule is estimated to be 90 kcal/mole less stable than benzene, but the activation of this highly exothermic transformation is a surprisingly high 33 kcal/mol, making it persistent at room temperature.[5]

The substituted derivative hexamethylprismane (in which all six hydrogens are substituted by

methyl groups) has a higher stability, and was synthesized by rearrangement reactions in 1966.[6]

Synthesis

Synthesis of Prismane:[7][8][9]

The synthesis starts from

biradical which forms prismane (6) and nitrogen with a yield of less than 10%. The compound was isolated by preparative gas chromatography
.

See also

References

  1. ISBN 978-0-85404-182-4
    . The name prismane is not longer recommended.
  2. doi:10.1002/cber.18690020171
    .
  3. doi:10.1021/ja00789a084
    .
  4. doi:10.1039/b109067d
    .
  5. doi:10.1002/anie.196907811
    .
  6. doi:10.1021/ja00976a046
    .
  7. ^ "Synthesis of Prismane".
  8. doi:10.1021/ja00789a084
    .
  9. doi:10.1021/ja00744a045
    .

External links
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