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Infrared spectroscopy of neutral and cationic pyrrolidine monomer in supersonic jet
胡勇军1,2
1.激光生命科学教育部重点实验室;2.华南师范大学光子学学院激光生命科学研究所, 广州光谱分析与功能探针重点实验室, 广州510631
Abstract:
Pyrrolidine (PRL) is a common five membered heterocyclic molecule in organism. In this study, the infrared spectra of pyrrolidine monomer in neutral and caionic states were obtained by Vacuum Ultraviolet (VUV) ionization, infrared photodissociation and time of flight mass spectrometry. Both in neutral and cationic states, it is found that their CH stretching vibration bands are red shifted. In the IR spectrum of neutral PRL, because the electric dipole moment of NH is small, we have not observed the NH stretching vibration bands. However, the NH stretching vibration band of PRL is greatly enhanced after ionization, and this band red shift compared with the precious experiment. It is found that the red shifts of CH stretching vibrations in neutral and cationic states are caused by the negative and positive hyperconjugation, respectively. The enhancement and red shift of the NH stretching band are caused by the ejection of the electrons on the N atom after ionization. Through the calculation of the gas phase acidity and deprotonation process of cationic PRL, it is found that the acidity of the CH bond is stronger than that of NH bond. These kinds of studies would be helpful to understand the intrinsic properties of biomolecules in neutral and cationic states, and to provide reference for the further study of living organic macromolecules.
Key words:  IR spectroscopy, hyperconjugation, cationic state, CH bond acidity, gas phase
FundProject:
超声分子束中中性态和离子态吡咯烷的红外光谱
胡勇军1,2
1.激光生命科学教育部重点实验室;2.华南师范大学光子学学院激光生命科学研究所, 广州光谱分析与功能探针重点实验室, 广州510631
摘要:
吡咯烷是生物体中常见的五元杂环分子。本研究应用真空紫外光电离结合红外光解离以及飞行时间质谱技术获得超声分子束中吡咯烷单体在中性态和离子态的红外光谱。实验光谱研究发现,吡咯烷在中性态和离子态的CH伸缩振动均有不同程度的红移现象。在中性态吡咯烷中,由于NH的电偶极矩较小我们没有观察到NH伸缩振动峰。而电离后的吡咯烷NH伸缩振动峰有很大的增强,并与其他实验相比出现红移现象。通过理论计算我们发现中性态和离子态的CH伸缩振动的红移分别是由反超共轭和正超共轭现象引起的。而NH峰的增强和红移则是由于N原子上的电子被电离所引起的。通过计算分子的气态酸碱度以及去质子化过程,发现在离子态中,CH的酸性比NH的酸性更强。本研究有助于深入了解生物分子在中性态和离子态的固有特性,为更深入的研究生命有机大分子提供参考依据。
关键词:  红外光谱,超共轭现象,离子态,CH键的酸性,气态
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