-(CH2)4-

from The Collaborative International Dictionary of English v.0.48

Butylene \Bu"ty*lene\, n. [From {Butyl}.]
   1. (Chem.) Any one of three metameric hydrocarbons, {C4H8},
      of the ethylene series. They are gaseous or easily
      liquefiable; -- called also {butene}.
      [1913 Webster]

   2. the hypothetical divalent radical {-(CH2)4-}; -- used in
      combining forms; as, butylene diamine.
      [PJC]