code: public int getNumericalBondOrder() {
  		if (value_order.equals("SING")) {
  			return 1;
  		} else if (value_order.equals("DOUB")) {
  			return 2;
  		} else if (value_order.equals("TRIP")) {
  			return 3;
  		} else if (value_order.equals("QUAD")) {
  			return 4;
  		} else {
  			logger.error("Unknown or non-numeric value for value_order: "
  					+ value_order);
  			return -1;
  		}
  	}
docs: Converts this ChemCompBond's value_order attribute into an int using the
  conversion:
  
  <pre>
  SING -> 1
  DOUB -> 2
  TRIP -> 3
  QUAD -> 4
  </pre>
  
  Any other values will return -1.
  <p>
  (Source:
  http://mmcif.rcsb.org/dictionaries/mmcif_mdb.dic/Items/_chem_comp_bond.
  value_order.html)
  
  @return the numerical value of this ChemCompBond's bond order, or -1 if
  the value is non-numeric or unknown.