prov:value
| - wherein R, R1, R2, R3, and R4 each, independently of the others, is an alkyl group, an aryl group, an arylalkyl group, or an alkylaryl group as further defined hereinabove, and wherein R, R1, R2, R3, and R4 each can be joined to a phenyl moiety to form a ring, each R???a, R???b, and R???c, independently of the others, is a halogen atom, an alkyl group, an alkoxy group, a nitrile group, a nitro gro
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