| 556 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {3} |
| 1 | DF | .~ HEAVY METAL CONTAINING (e.g., Ga, In or T1, etc.) {19} |
| 51 | DF | .~.~ Titanium, zirconium, or hafnium containing (Ti, Zr, or Hf) {2} |
| 54 | DF | .~.~.~ Plural chalcogens bonded directly to the metal (e.g., alkyl titanates, titanic esters, etc.) {2} |
| 56 | | .~.~.~.~ Nitrogen or halogen containing |