Tetramethylbutane
Introduction '''Tetramethylbutane''', sometimes called '''hexamethylethane''', is a hydrocarbon with formula C8H18 or (H3C-)3C-C(-CH3)3.It is the most heavily branched and most compact of the many octane isomers, the only one with a butane (C4) 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. (Among cyclic hydrocarbons, cubane, C8H8 is even smaller and is also solid at room temperature.) 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 (electron correlation) between the methyl groups (protobranching).The compound can be obtained from ethyl bromide, ''tert''-butyl bromide, and magnesium metal in the presence of manganese(II) ions. Despite conditions amenable to the formation of a Grignard reagent, organomagnesium compounds are believed not 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".
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