| 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 |  | .~.~.~.~ 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} | 
| 544 | DF | .~.~.~.~.~> And chalcogen bonded directly to a ring carbon of the five membered hetero ring which is not adjacent to the ring nitrogen (e.g., 2,4 pyrrolidinediones, etc.) | 
| 545 | DF | .~.~.~.~.~> And chalcogen bonded directly to the other ring carbon of the five-membered hetero ring which is adjacent to the ring nitrogen (e.g., succinimide, etc.) {3} | 
| 550 | DF | .~.~.~.~.~> Nitrogen attached directly or indirectly to the five-membered hetero ring by acyclic nonionic bonding | 
| 551 | DF | .~.~.~.~.~> Chalcogen attached indirectly to the five-membered hetero ring by acyclic nonionic bonding | 
| 552 | DF | .~.~.~.~.~> Processes of forming 2-pyrrolidone which is unsubstituted or alkyl or alkenyl substituted only {2} | 
| 555 | DF | .~.~.~.~.~> Purification or recovery of 2-pyrrolidone which is unsubstituted or alkyl substituted only |