| 540 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
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| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {1} |
| 1 | DF | .~ HETEROCYCLIC CARBON COMPOUNDS CONTAINING A HETERO RING HAVING CHALCOGEN (I.E., OXYGEN, SULFUR, SELENIUM OR TELLURIUM) OR NITROGEN AS THE ONLY RING HETERO ATOMS {6} |
| 200 | DF | .~.~ Hetero ring is four-membered containing nitrogen and having chalcogen double bonded directly to a ring carbon which is adjacent to the ring nitrogen {7} |
| 354 | DF | .~.~.~ Additional chalcogen bonded directly to the hetero ring {5} |
| 358 |  | .~.~.~.~ The additional chalcogen is sulfur which is bonded directly to chalcogen {1} |
| 359 | DF | .~.~.~.~.~> The sulfur is double bonded directly to the chalcogen |