prov:value
| - In this case, R2 and R3 are, independently of each other, hydrogen or methyl, R4 is an aliphatic or alicyclic hydrocarbon group such as an alkyl, alkenyl, cycloalkyl or cycloalkenyl group, an aromatic hydrocarbon group, the carbon atom of which may be substituted by a nitrogen atom (a hydrogen atom on the aromatic ring may be substituted by a hydrocarbon group), such as a phenyl, pyridyl, benzyl,
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