| 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} |
| 576 | DF | .~.~.~ Polycyclo ring system which contains the hetero ring as one of the cyclos {4} |
| 586 |  | .~.~.~.~ Tricyclo ring system which contains the hetero ring as one of the cyclos {1} |
| 587 | DF | .~.~.~.~.~> The hetero ring shares ring members with each of two benzene rings in the tricyclo ring system (e.g., morphanthridines, etc.) {1} |