code: public static double getMolecularWeight(HELM2Notation helm2notation) throws BuilderMoleculeException, CTKException, ChemistryException {
      /* First build one big molecule; List of molecules? */
      List<AbstractMolecule> molecules = buildMolecule(helm2notation);
      return calculateMolecularWeight(molecules);
    }
docs: method to get the molecular weight for the whole HELM
  
  @param helm2notation input HELM2Notation
  @return MolecularWeight of the whole HELM
  @throws BuilderMoleculeException if the whole molecule can not be built
  @throws CTKException general ChemToolKit exception passed to HELMToolKit
  @throws ChemistryException if the Chemistry Engine can not be initialized