| 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} |
| 553 | DF | .~.~.~ The hetero ring contains plural nitrogens (e.g., 1,3-diazepines, etc.) {3} |
| 555 | DF | .~.~.~.~ Polycyclo ring system which contains the hetero ring as one of the cyclos {3} |
| 557 | DF | .~.~.~.~.~ Tricyclo ring system which contains the hetero ring as one of the cyclos {1} |
| 558 | DF | .~.~.~.~.~.~ Nitrogen of the hetero ring is shared by an additional cyclo of the tricyclo ring system {5} |
| 559 |  | .~.~.~.~.~.~.~ The additional cyclo has at least six ring members |