| 548 / | 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) {4} |
| 400 | DF | .~.~ Hetero ring is five-membered consisting of one nitrogen and four carbons (e.g., halopyrrolidines, etc.) {20} |
| 541 | DF | .~.~.~ Chalcogen attached directly to the five-membered hetero ring by nonionic bonding (e.g., 3-pyrrolidinols, etc.) {3} |
| 543 | DF | .~.~.~.~ Chalcogen bonded directly to a ring carbon of the five-membered hetero ring which is adjacent to the ring nitrogen (e.g., 2-pyrrolidones, etc.) {6} |
| 555 |  | .~.~.~.~.~ Purification or recovery of 2-pyrrolidone which is unsubstituted or alkyl substituted only |