prov:value
| - up, a mercapto group, a nitroso group, a halogen atom, a nitro group, a sulfone group, or an acyl group, wherein one or more of R6, R7, R8, R9, R10, and R11 can be absent if a ring carbon atom has a double bond or a triple bond to another R group or to another ring carbon atom, and R12 and R13 each, independently of the other, is a hydrogen atom, an alkyl group, an aryl group, an arylalkyl group,
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