prov:value
| - R1, R2, R3, and R4 are individually hydrogen; saturated aliphatic of from 1 to 10 carbon atoms, for example, propyl, t-butyl, heptyl, and the like; aryl of from 6 to 10 carbon atoms, for example, phenyl and naphthyl; or halo such as chloro, fluoro, and the like; or R1 and R2 or R3 and R4 taken together comprise the atoms necessary to complete a fused aromatic ring optionally bearing at least one s
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