| 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} |
| 231 | DF | .~.~.~ Cyclic anhydrides (i.e., -C(=X)OC(=X)-, wherein the X's are the same or diverse chalcogens, is part of the hetero ring) {2} |
| 233 | DF | .~.~.~.~ The cyclic anhydride is five-membered (e.g., succinic anhydride, etc.) {7} |
| 234 | DF | .~.~.~.~.~ Polycyclo ring system having the cyclic anhydride as one of the cyclos {3} |
| 240 | DF | .~.~.~.~.~.~ Bicyclo ring system having the cyclic anhydride as one of the cyclos {5} |
| 247 | DF | .~.~.~.~.~.~.~ Phthalic anhydride per se {2} |
| 250 | DF | .~.~.~.~.~.~.~.~ Purification or recovery {1} |
| 251 |  | .~.~.~.~.~.~.~.~.~ By chemical reaction of impurity in presence of added chemical substance |