| 544 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
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| * | DD | ORGANIC COMPOUNDS (Class 532, subclass 1) {1} |
| * | DD | .~ HETEROCYCLIC CARBON COMPOUNDS CONTAINING A HETERO RING HAVING CHALCOGEN (I.E., OXYGEN, SULFUR, SELENIUM, OR TELLURIUM) OR NITROGEN AS THE ONLY RING HETERO ATOMS (Class 540, subclass 1) {1} |
| 1 | DF | .~.~ Hetero ring is six-membered having two or more ring hetero atoms of which at least one is nitrogen (e.g., selenazines, etc.) {6} |
| 224 | DF | .~.~.~ The six-membered hetero ring consists of two nitrogens and four carbons (e.g., 1,2-diazines, etc.) {9} |
| 225 | DF | .~.~.~.~ Heavy metal or aluminum containing {2} |
| 226 |  | .~.~.~.~.~ Arsenic or zinc containing |