| 568 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {4} |
| 300 | DF | .~ OXYGEN CONTAINING (E.G., PERCHLORYLBENZENE, ETC.) {11} |
| 301 | DF | .~.~ Ketenes (e.g., halogenated ketenes, etc.) {1} |
| 302 | | .~.~.~ Ketene per se (i.e., HCH=C=O) |