| 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} |
| 484 | DF | .~.~ The hetero ring contains seven members including nitrogen and carbon {14} |
| 596 | DF | .~.~.~ Additional hetero ring attached directly or indirectly to the hetero ring by nonionic bonding {2} |
| 602 | DF | .~.~.~.~ The additional hetero ring is five-membered and contains nitrogen {1} |
| 603 |  | .~.~.~.~.~ Plural hetero atoms in the additional hetero ring |