| 549 / | 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) {2} | 
| 200 | DF | .~.~ Oxygen containing hetero ring (e.g., dioxirane, etc.) {16} | 
| 512 | DF | .~.~.~ The hetero ring is three-membered consisting of one oxygen and two carbons {7} | 
| 554 | DF | .~.~.~.~ Chalcogen attached indirectly to the hetero ring by nonionic bonding {2} | 
| 561 | DF | .~.~.~.~.~ The chalcogen, X, is part of a -C(=X)X- group, wherein the X's are the same or diverse chalcogens {1} | 
| 562 |  | .~.~.~.~.~.~ Additional -C(=X)- or other sulfur attached indirectly to the hetero ring |