C8H18

from The Collaborative International Dictionary of English v.0.48

octane \oc"tane\ ([o^]k"t[=a]n), n. [See {Octa-}] (Chem.)
   Any one of a group of metametric hydrocarbons ({C8H18}) of
   the methane (paraffin) series. The most important is a
   colorless, volatile, inflammable liquid, found in petroleum,
   and a constituent of gasoline or ligroin.
   [1913 Webster +PJC]

from The Collaborative International Dictionary of English v.0.48

dibutyl \di*bu"tyl\ (d[-i]*b[=u]"t[i^]l), n. [Pref. di- +
   butyl.] (Chem.)
   A liquid hydrocarbon, {C8H18}, of the alkane series, being
   one of several octanes, and consisting of two butyl radicals.
   Cf. {Octane}.
   [1913 Webster]