code: public static IAtomContainer makePyrroleAnion() {
          IAtomContainer mol = new AtomContainer();
          IAtom nitrogenAnion = new Atom("N");
          nitrogenAnion.setFormalCharge(-1);
          mol.addAtom(new Atom("C")); // 0
          mol.addAtom(nitrogenAnion); // 1
          mol.addAtom(new Atom("C")); // 2
          mol.addAtom(new Atom("C")); // 3
          mol.addAtom(new Atom("C")); // 4
  
          mol.addBond(0, 1, IBond.Order.SINGLE); // 1
          mol.addBond(1, 2, IBond.Order.SINGLE); // 2
          mol.addBond(2, 3, IBond.Order.DOUBLE); // 3
          mol.addBond(3, 4, IBond.Order.SINGLE); // 4
          mol.addBond(4, 0, IBond.Order.DOUBLE); // 5
  
          return mol;
      }
docs: Returns pyrrole anion without explicit hydrogens.
  
  @cdk.inchi InChI=1/C4H4N/c1-2-4-5-3-1/h1-4H/q-1