E and Z stereoisomers of compounds of the phthalide series
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The stereospecific position of the H4 proton in the PMR spectra of 3-benzyl-idenephthalides identifies unambiguously the E and Z isomers in a mixture. The IR spectra of off-planar deformation vibrations of the C=C bond in the 990–970 cm−1 region have strong absorption bands, assigned to the E and Z isomers. The strong short-wave band (260 nm) for 3-benzylidenephthalides, having only one benzene ring in the indan moiety, suggests the presence of the E form (ε=28,000). The long-wave absorption band at 390–430 nm belongs to the Z isomers (ε=21,000–31,000). 3-Benzylidenephthalides which have no carbonyl groups in their molecules, show fluorescence (λf1=540–560 nm in EtOH).
Keywords3-benzylidenephthalides E and Z isomers PMR, IR, and UV spectra
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