New sub-monomer synthetic methods for the preparation of peptide nucleic acid oligomeric structures are disclosed that provide for the synthesis of both predefined sequence peptide nucleic acid oligomers as well as random sequence peptide nucleic acid oligomers. Further these methods also provide for the incorporation of peptide nucleic acid units or strings of such units with amino acids or strings of amino acids in chimeric peptide nucleic acid-amino acid compounds. Further disclosed are methods of making random libraries of peptide nucleic acids using the fully preformed monomers.