Cubane

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Cubane
Structural formula of cubane
Structural formula of cubane
Ball-and-stick model of cubane
Ball-and-stick model of cubane
Names
Preferred IUPAC name
Cubane[1]
Systematic IUPAC name
Pentacyclo[4.2.0.02,5.03,8.04,7]octane
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
UNII
  • InChI=1S/C8H8/c1-2-5-3(1)7-4(1)6(2)8(5)7/h1-8H checkY
    Key: TXWRERCHRDBNLG-UHFFFAOYSA-N checkY
  • InChI=1/C8H8/c1-2-5-3(1)7-4(1)6(2)8(5)7/h1-8H
    Key: TXWRERCHRDBNLG-UHFFFAOYAL
  • C12C3C4C1C5C2C3C45
Properties
C8H8
Molar mass 104.15 g/mol
Appearance Transparent[2] crystalline solid
Density 1.29 g/cm3
Melting point 133.5 °C (272.3 °F; 406.6 K)[3]
Boiling point 161.6 °C (322.9 °F; 434.8 K)[3]
Related compounds
Related hydrocarbons
Prismane C8
Related compounds
Octafluorocubane
Octanitrocubane
Octaazacubane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Cubane is a synthetic

kinetically stable, due to a lack of readily available decomposition paths. It is the simplest hydrocarbon with octahedral symmetry
.

Having high potential energy and 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 smaller amount of space, an important consideration for applications in fuel storage and energy transport. Furthermore, their geometry and stability make them suitable isosteres for benzene rings.[7]

Synthesis

The classic 1964 synthesis starts with the conversion of

2-cyclopentenone to 2-bromocyclopentadienone:[4][8]

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. One ketal of the endo isomer is subsequently selectively deprotected with aqueous hydrochloric acid
to 3.

In the next step, the endo isomer 3 (with both

) 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).

A more approachable laboratory synthesis of disubstituted cubane involves bromination of the ethylene ketal of cyclopentanone to give a tribromocyclopentanone derivative. Subsequent steps involve dehydrobromination, Diels-Alder dimerization, etc.[9][10]

Alternative synthesis of a disubstituted cubane

The resulting cubane-1,4-dicarboxylic acid is used to synthesize other substituted cubanes. Cubane itself can be obtained nearly quantitatively by photochemical decarboxylation of the thiohydroxamate ester (the Barton decarboxylation).[11]

Derivatives

The synthesis of the octaphenyl

pyramidalized geometry. At the time of its synthesis, this was the most pyramidalized alkene to have been made.[17] 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.[18]

In 2022, both

anion C
8
F
8
, with a free electron trapped inside the cube, in effect making it the world's smallest box.[21]

Cubylcubanes and oligocubanes

Cubene (1,2-dehydrocubane) and 1,4-cubanediyl(1,4-dehydrocubane) are enormously strained compounds which both undergo

Penn State University showed that poly-cubane synthesized by solid-state reaction is 100% sp3 carbon bonded with a tetrahedral angle (109.5°) and exhibits exceptional optical properties (high refractive index).[24]

Reactions

With a rhodium catalyst, it first forms syn-tricyclooctadiene, which can thermally decompose to cyclooctatetraene at 50–60 °C.[27]

See also

References

External links

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