| 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 |  | .~.~.~ The hetero ring contains plural nitrogens (e.g., 1,3-diazepines, etc.) {3} |
| 554 | DF | .~.~.~.~> The hetero ring contains at least three nitrogens |
| 555 | DF | .~.~.~.~> Polycyclo ring system which contains the hetero ring as one of the cyclos {3} |
| 575 | DF | .~.~.~.~> The nitrogens are in the 1,4-positions of the hetero ring |