code: private void setActiveCenters(IAtomContainer reactant) throws CDKException {
          HOSECodeGenerator hcg = new HOSECodeGenerator();
          Iterator<IAtom> atomis = reactant.atoms().iterator();
          while (atomis.hasNext()) {
              IAtom atomi = atomis.next();
              if (reactant.getConnectedSingleElectronsCount(atomi) == 1) {
  
                  hcg.getSpheres(reactant, atomi, 5, true);
                  Iterator<IAtom> atomls = hcg.getNodesInSphere(5).iterator();
                  while (atomls.hasNext()) {
                      IAtom atoml = atomls.next();
                      if (atoml != null && !atoml.getFlag(CDKConstants.ISINRING)
                              && (atoml.getFormalCharge() == CDKConstants.UNSET ? 0 : atoml.getFormalCharge()) == 0
                              && !atoml.getSymbol().equals("H") && reactant.getMaximumBondOrder(atoml) == IBond.Order.SINGLE) {
  
                          Iterator<IAtom> atomhs = reactant.getConnectedAtomsList(atoml).iterator();
                          while (atomhs.hasNext()) {
                              IAtom atomh = atomhs.next();
                              if (atomh.getSymbol().equals("H")) {
                                  atomi.setFlag(CDKConstants.REACTIVE_CENTER, true);
                                  atoml.setFlag(CDKConstants.REACTIVE_CENTER, true);
                                  atomh.setFlag(CDKConstants.REACTIVE_CENTER, true);
                                  reactant.getBond(atomh, atoml).setFlag(CDKConstants.REACTIVE_CENTER, true);
                              }
                          }
                      }
                  }
              }
          }
      }
docs: set the active center for this molecule.
  The active center will be those which correspond with [A*]-(C)_5-C6[H]
  <pre>
  C: Atom with single electron
  C6: Atom with Hydrogen
  </pre>
  
  @param reactant The molecule to set the activity
  @throws CDKException