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首页> 外文期刊>RSC Advances >A pair of Schiff base enantiomers studied by absorption, fluorescence, electronic and vibrational circular dichroism spectroscopies and density functional theory calculation
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A pair of Schiff base enantiomers studied by absorption, fluorescence, electronic and vibrational circular dichroism spectroscopies and density functional theory calculation

机译：通过吸收，荧光，电子和振动圆形二色分子和密度泛函理论计算研究了一对席夫碱对映体研究

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2-(((1 R ,2 S )-2-Hydroxy-1,2-diphenylethylimino)methyl)phenol and 2-(((1 S ,2 R )-2-hydroxy-1,2-diphenylethylimino)methyl)phenol have been synthesized as a pair of enantiomeric Schiff bases of a chiral salicylaldehyde. These compounds were subsequently characterized by melting point, EI-MS, IR, ~(1) H-NMR and X-ray crystallographic analyses. The UV-vis absorption, fluorescent emission, electronic and vibrational circular dichroism (ECD and VCD) spectral properties of these enantiomers were determined in solution in a variety of different solvents, including acetonitrile, ethanol and hexane, as well as being determined in the solid state. The effects of the different solvents were evaluated in detail, and it was found that the enol-imine tautomer existed as the dominant species in nonpolar solvents, such as hexane, and that the enol-imine and keto-enamine tautomers coexisted in polar solvents, such as ethanol. Theoretical IR and VCD spectra of the enantiomers were calculated at the B3LYP/6-311+G(d,p) level by density functional theory. Given that the different tautomers coexisted in solution and VCD is very sensitive to conformational changes, it was not possible to reliably determine the absolute configurations of the enantiomers based on their solution phase VCD spectra. However, the calculated IR and VCD spectra in a vacuum were in good agreement with the experimental solid state spectra, and it was therefore possible to reasonably assign the absolute configurations of the enantiomers based on the VCD calculations. This study therefore represents a good example of the practical application of solid state VCD spectra to assign the absolute configurations of different enantiomers.
机译：2 - （（（1R，2 s）-2-羟基-1,2-二苯基乙基咪啶）甲基）苯酚和2 - （（（1s，2 r）-2-羟基-1,2-二苯基乙基乙基咪啶）甲基）苯酚已被合成为手性水杨醛的一对对映体Schiff碱基。随后通过熔点，EI-MS，IR，〜（1）H-NMR和X射线晶体分析来表征这些化合物。这些对映体的UV-Vis吸收，荧光发射，电子和振动圆形二色性（ECD和VCD）在各种不同溶剂中的溶液中测定，包括乙腈，乙醇和己烷，以及在固体中测定状态。详细评估了不同溶剂的效果，发现烯醇酰亚胺互变异构成非极性溶剂中的优势物质，例如己烷，烯醇 - 亚胺和酮烯酮互变异构体在极性溶剂中共存，如乙醇。通过密度泛函理论，在B3LYP / 6-311 + G（D，P）水平下计算对映体的理论IR和VCD光谱。鉴于在溶液和VCD中共存的不同互变异构致敏感性变化非常敏感，不可能基于其溶液VCD光谱可靠地确定对映体的绝对配置。然而，在真空中计算的IR和VCD光谱与实验固态光谱有良好的一致性，因此可以基于VCD计算合理地分配对映体的绝对构型。因此，该研究代表了固态VCD光谱的实际应用的良好举例，以分配不同对映体的绝对构型。

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