Hydrophobic side chains
  (R groups) consist almost
   entirely of C and H atoms.

   These amino acids tend to
   form the inner core of soluble
   proteins, buried away from the
   aqueous external medium.

   They also play an important
   role in membranes associating
   with the inner fatty acid
   hydrophobic center.

  Aromatic amino acids:
  contain R groups with ring
  structures [PHE, TYR, TRP]