Cubane

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Cubane
Structural formula of cubane
Ball-and-stick model of cubane
Names
IUPAC name
Cubane[1]
Other names
Pentacyclo[4.2.0.02,5.03,8.04,7]octane
Identifiers
277-10-1 YesY
ChEBI CHEBI:33014 YesY
ChemSpider 119867 YesY
Jmol 3D model Interactive image
PubChem 136090
Properties
C8H8
Molar mass 104.15 g/mol
Density 1.29 g/cm3
Melting point 133.5 °C (272.3 °F; 406.6 K)[2]
Boiling point 161.6 °C (322.9 °F; 434.8 K)[2]
Related compounds
Related hydrocarbons
Cuneane
Dodecahedrane
Tetrahedrane
Prismane
Prismane C8
Related compounds
Heptanitrocubane
Octanitrocubane
Octaazacubane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cubane (C8H8) is a synthetic hydrocarbon molecule that consists of eight carbon atoms arranged at the corners of a cube, with one hydrogen atom attached to each carbon atom. A solid crystalline substance, cubane is one of the Platonic hydrocarbons and a member of the prismanes. It was first synthesized in 1964 by Philip Eaton and Thomas Cole.[3] Prior to this work, researchers believed that cubic carbon-based molecules would be too unstable to exist. The cubic shape requires the carbon atoms to adopt an unusually sharp 90° bonding angle, which would be highly strained as compared to the 109.45° angle of a tetrahedral carbon. Once formed, cubane is quite kinetically stable, due to a lack of readily available decomposition paths.

Having high energy but kinetic stability makes cubane and its derivative compounds useful for controlled energy storage. For example, octanitrocubane and heptanitrocubane have been studied as high-performance explosives.

These compounds also typically have a very high density for hydrocarbon molecules. The resulting high energy density means a large amount of energy can be stored in a comparably small amount of space, an important consideration for applications in fuel storage and energy transport.

Synthesis[edit]

The classic 1964 synthesis starts with the conversion of 2-cyclopentenone to 2-bromocyclopentadienone:[3][4]

Cyclopentenone to 2-bromocyclopentadienone.png

Allylic bromination with N-bromosuccinimide in carbon tetrachloride followed by addition of molecular bromine to the alkene gives a 2,3,4-tribromocyclopentanone. Treating this compound with diethylamine in diethyl ether causes elimination of two equivalents of hydrogen bromide to give the diene product.

Eaton's 1964 synthesis of cubane

The construction of the eight-carbon cubane framework begins when 2-bromocyclopentadienone undergoes a spontaneous Diels-Alder dimerization, analogous to the dimerization of cyclopentadiene to dicyclopentadiene—two molecules of 1 react to form 2. For the subsequent steps to succeed, only the endo isomer is useful, and this is the predominant isomer formed in this reaction. This is the most likely product as a result of minimized steric interactions between the bromine of each molecule with the bromine and carbonyl of the other when the reactants approach each other and minimized like-dipole interactions in the transition state of the reaction itself. Both carbonyl groups are protected as acetals with ethylene glycol and p-toluenesulfonic acid in benzene; one acetal is then selectively deprotected with aqueous hydrochloric acid to 3.

In the next step, the endo isomer 3 (with both alkene groups in close proximity) forms the cage-like isomer 4 in a photochemical [2+2] cycloaddition. The bromoketone group is converted to ring-contracted carboxylic acid 5 in a Favorskii rearrangement with potassium hydroxide. Next, the thermal decarboxylation takes place through the acid chloride (with thionyl chloride) and the tert-butyl perester 6 (with tert-butyl hydroperoxide and pyridine) to 7; afterward, the acetal is once more removed in 8. A second Favorskii rearrangement gives 9, and finally another decarboxylation gives, via 10, cubane (11).

Derivatives[edit]

The synthesis of the octaphenyl derivative from tetraphenylcyclobutadiene nickel bromide by Freedman in 1962 pre-dates that of the parent compound.[2][5][6][7] A "hypercubane", with a hypercube-like structure, was predicted to exist in a 2014 publication.[8][9] Two different isomers of cubene have been synthesized, and a third analyzed computationally. The alkene in ortho-cubene is exceptionally reactive due to its pyramidalized geometry. At the time of its synthesis, this was the most pyramidalized alkene to have been successfully made.[10] The meta-cubene isomer is even less stable, and the para-cubene isomer probably only exists as a diradical rather than an actual diagonal bond.[11]

Reactions[edit]

Cuneane may be produced from cubane by a metal-ion-catalyzed σ-bond rearrangement.[12][13]

See also[edit]

References[edit]

  1. ^ According to page 41 of a 2004 IUPAC guide, cubane is the "preferred IUPAC name."
  2. ^ a b c Biegasiewicz, Kyle; Griffiths, Justin; Savage, G. Paul; Tsanakstidis, John; Priefer, Ronny (2015). "Cubane: 50 years later". Chemical Reviews 115: 6719–6745. doi:10.1021/cr500523x. 
  3. ^ a b Eaton, Philip E.; Cole, Thomas W. (1964). "Cubane". J. Am. Chem. Soc. 86 (15): 3157–3158. doi:10.1021/ja01069a041. 
  4. ^ Eaton, Philip E.; Cole, Thomas W. (1964). "The Cubane System". J. Am. Chem. Soc. 86 (5): 962–964. doi:10.1021/ja01059a072. 
  5. ^ Freedman, H. H. (1961). "Tetraphenylcyclobutadiene Derivatives. II.1 Chemical Evidence for the Triplet State". J. Am. Chem. Soc. 83 (9): 2195–2196. doi:10.1021/ja01470a037. 
  6. ^ Freedman, H. H.; Petersen, D. R. (1962). "Tetraphenylcyclobutadiene Derivatives. IV.1 “Octaphenylcubane”; A Dimer of Tetraphenylcyclobutadiene". J. Am. Chem. Soc. 84 (14): 2837–2838. doi:10.1021/ja00873a046. 
  7. ^ Pawley, G. S.; Lipscomb, W. N.; Freedman, H. H. (1964). "Structure of the Dimer of tetraphenylcyclobutadiene". J. Am. Chem. Soc. 86 (21): 4725–4726. doi:10.1021/ja01075a042. 
  8. ^ Pichierri, F. (2014). "Hypercubane: DFT-based prediction of an Oh-symmetric double-shell hydrocarbon". Chem. Phys. Lett. 612: 198–202. doi:10.1016/j.cplett.2014.08.032. 
  9. ^ http://www.compchemhighlights.org/2014/12/hypercubane-dft-based-prediction-of-oh.html
  10. ^ Eaton, Philip E.; Maggini, Michele (1988). "Cubene (1,2-dehydrocubane)". J. Am. Chem. Soc. 110 (21): 7230–7232. doi:10.1021/ja00229a057. 
  11. ^ Minyaev, Ruslan M.; Minkin, Vladimir I.; Gribanova, Tatyana N. (2009). "2.3 A Theoretical Approach to the Study and Design of Prismane Systems". In Dodziuk, Helena. Strained Hydrocarbons. Wiley. p. 55. ISBN 9783527627141. 
  12. ^ Smith, Michael B.; March, Jerry (2001). March’s Advanced Organic Chemistry (5th ed.). John Wiley & Sons. p. 1459. ISBN 0-471-58589-0. 
  13. ^ Kindler, K.; Lührs, K. (1966). Chem. Ber. 99: 227.  Missing or empty |title= (help)

External links[edit]