prov:value
| - R1 and R2 are identical or different and are each a hydrogen atom, a C1-C10-alkyl group, a C1-C10-alkoxy group, a C6-C20-aryl group, a C6-C10-aryloxy group, a C2-C10-alkenyl group, an OH group, an NR12 2 group, where R12 is a C1-C10-alkyl group or a C6-C14-aryl group, or a halogen atom,
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