prov:value
| - wherein X1, X2, X3, and X4 each, independently of the others, is a hydrogen atom, a halogen atom (including fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms), a hydroxy group, an amine group (including primary, secondary, and tertiary amine groups), an ammonium group, a cyano group, a pyridine group, a pyridinium group, an ether group, a carbonyl group, a thiocarbonyl group, an alde
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