Hexamethylbenzene

Hexamethylbenzene
Structural formula of hexamethylbenzene
Ball-and-stick model of the hexamethylbenzene molecule
Names
Preferred IUPAC name
Hexamethylbenzene
Other names
1,2,3,4,5,6-Hexamethylbenzene
Mellitene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.001.616 Edit this at Wikidata
UNII
  • InChI=1S/C12H18/c1-7-8(2)10(4)12(6)11(5)9(7)3/h1-6H3 ☒N
    Key: YUWFEBAXEOLKSG-UHFFFAOYSA-N ☒N
  • InChI=1/C12H18/c1-7-8(2)10(4)12(6)11(5)9(7)3/h1-6H3
    Key: YUWFEBAXEOLKSG-UHFFFAOYAF
  • c1(c(c(c(c(c1C)C)C)C)C)C
Properties
C12H18
Molar mass 162.276 g·mol−1
Appearance White crystalline powder
Density 1.0630 g cm−3
Melting point 165.6 ± 0.7 °C
Boiling point 265.2 °C (509.4 °F; 538.3 K)
insoluble
Solubility acetic acid, acetone, benzene, chloroform, diethyl ether, ethanol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula C12H18 and the condensed structural formula C6(CH3)6. It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929, Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat[1] and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a historically significant result, both for the field of X-ray crystallography and for understanding aromaticity.[2][3]

Hexamethylbenzene can be oxidised to mellitic acid,[4] which is found in nature as its aluminium salt in the rare mineral mellite.[5] Hexamethylbenzene can be used as a ligand in organometallic compounds.[6] An example from organoruthenium chemistry shows structural change in the ligand associated with changes in the oxidation state of the metal centre,[7][8] though the same change is not observed in the analogous organoiron system.[7]

In 2016 the crystal structure of the hexamethylbenzene dication C
6(CH
3)2+
6 was reported in Angewandte Chemie International Edition,[9] showing a pyramidal structure in which a single carbon atom has a bonding interaction with six other carbon atoms.[10][11] This structure was "unprecedented",[9] as the usual maximum valence of carbon is four, and it attracted attention from New Scientist,[10] Chemical & Engineering News,[11] and Science News.[12] The structure does not violate the octet rule since the carbon–carbon bonds formed are not two-electron bonds, and is pedagogically valuable for illustrating that a carbon atom "can [directly bond] with more than four atoms".[12] Steven Bachrach has demonstrated that the compound is hypercoordinated but not hypervalent, and also explained its aromaticity.[13] The idea of describing the chemical bonding in compounds and chemical species in this way through the lens of organometallic chemistry was proposed in 1975,[14] soon after the dication C
6(CH
3)2+
6 was first observed.[15][16][17]

  1. ^ Lonsdale, Kathleen (1929). "The Structure of the Benzene Ring in Hexamethylbenzene". Proc. R. Soc. A. 123 (792): 494–515. doi:10.1098/rspa.1929.0081.
  2. ^ Cite error: The named reference Lydon1 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Lydon2 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference HMBoxidation was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference mellite was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference AreneReview was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Fe was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference RuHMB2 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference PyramidalAngewChem was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference PyramidalNewSci was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference PyramidalC&ENews was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference PyramidalSciNews was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Bachrach was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference HMBviaOMetChem was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference HMBcatObs1 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference HMBcatObs2 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference HMBcatObs3 was invoked but never defined (see the help page).