Tetramethylbutane
Tetramethylbutane, sometimes called hexamethylethane, is a hydrocarbon with formula C8H18 or 3C-C3. It is the most heavily branched and most compact of the octane isomers, the only one with a butane backbone. Because of its highly symmetrical structure, it has a very high melting point and a short liquid range; in fact, it is the smallest saturated acyclic hydrocarbon that appears as a solid at a room temperature of 25 °C. It is also the most stable C8H18 isomer, with a heat of formation lower than that of n-octane, a fact that has been attributed to stabilizing dispersive interactions between the methyl groups.
The compound can be obtained from ethyl bromide, tert-butyl bromide, and magnesium metal in the presence of manganese ions. Despite conditions amenable to the formation of a Grignard reagent, organomagnesium compounds are believed not to be the active species. Instead, they transmetalate to organomanganese compounds, which then decompose to tert-butyl radicals, which dimerize.
The full IUPAC name of the compound is 2,2,3,3-tetramethylbutane, but the numbers are superfluous in this case because there is no other possible arrangement of "tetramethylbutane".