CH3.CH2.NH2

Isomer \I"so*mer\ ([imac]"s[-o]*m[~e]r), n. [See {Isomeric}.]
   (Chem.)
   A compound which is isomeric with another body or compound; a
   compound having the same chemical composition as another
   compound; a member of an isomeric series.
   [1913 Webster +PJC]

   Note: An isomer may be a {structural isomer}, in which some
         of the atoms are bonded to different atoms (as in
         {CH3.CH2.NH2} and {CH3.NH.CH3}), or an {optical
         isomer}, in which the number and types of chemical
         bonds are identical, but the arrangement of the atoms
         in three-dimensional space is different; the latter are
         also called {stereoisomers}.
         [PJC]