| 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} |
| 2 | DF | .~.~ Cyclopentanohydrophenanthrene ring system containing {10} |
| 94 | DF | .~.~.~ Hetero ring attached directly to the cyclopentanohydrophenanthrene ring system by nonionic bonding {3} |
| 100 | DF | .~.~.~.~ The hetero ring contains plural chalcogens {1} |
| 101 |  | .~.~.~.~.~ The hetero ring and acyclic chalcogen are both bonded directly at the 17 position of the cyclopentanohydrophenanthrene ring system |