prov:value
| - R20 and R21 independently represent a hydrogen or halogen atom, e.g. chlorine, bromine, iodine, a lower alkyl group of 1 to 5 carbon atoms e.g. methyl, ethyl, and alkoxy group of 1 to 5 carbon atoms, e.g. methoxy, ethoxy, an aryl group of up to 7 carbon atoms, e.g. phenyl and aryloxy group of up to 7 carbon atoms e.g. phenoxy or R20 and R21 together represent the necessary atoms to form an aromati
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