Wikipedia
Tetramethylbutane, sometimes called hexamethylethane, is a hydrocarbon with formula CH or (HC-)C-C(-CH). 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.
The compound can be obtained by reaction of Grignard reagent tert-butylmagnesium bromide with ethyl bromide, or of ethylmagnesium bromide with tert-butyl bromide in the presence of manganese( II) ions. This transformation is believed to go through the dimerization of two tert-butyl radicals, which are generated by decomposition of the organomanganese compounds generated in situ.
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".