code: public static ILigand defineLigand(IAtomContainer container, VisitedAtoms visitedAtoms, int chiralAtom,
              int ligandAtom) {
          if (ligandAtom == HYDROGEN) {
              return new ImplicitHydrogenLigand(container, visitedAtoms, container.getAtom(chiralAtom));
          } else {
              return new Ligand(container, visitedAtoms, container.getAtom(chiralAtom), container.getAtom(ligandAtom));
          }
      }
docs: Creates a ligand attached to a single chiral atom, where the involved
  atoms are identified by there index in the {@link IAtomContainer}. For ligand
  atom, {@link #HYDROGEN} can be passed as index, which will indicate the presence of
  an implicit hydrogen, not explicitly present in the chemical graph of the
  given <code>container</code>.
  
  @param container  {@link IAtomContainer} for which the returned {@link ILigand}s are defined
  @param visitedAtoms a list of atoms already visited in the analysis
  @param chiralAtom an integer pointing to the {@link IAtom} index of the chiral atom
  @param ligandAtom an integer pointing to the {@link IAtom} index of the {@link ILigand}
  @return           the created {@link ILigand}