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采用Gaussian 03、SpecDis v1.58、Multiwfn 2.2.1、Molekel 5.4等软件对麻黄碱及其立体异构体的电子结构及电子圆二色谱(ECD谱)性质进行研究。计算结果表明:(1)电子密度拓扑分析证实麻黄碱及其立体异构体分子的H(7)与N(4)之间存在键鞍点,从该键鞍点出发存在连接H(7)、N(4)的键径,表明形成了分子内氢键。(2)研究获得了理论ECD谱。A1的ECD谱在(184、199、229)nm附近存在正性CD谱带;在188 nm、215 nm附近存在负性CD谱带。B1的ECD谱在184nm附近存在正性CD谱带,在187m附近存在负性CD谱带。C1的ECD谱在185nm、222nm附近存在正性CD谱带,在(192、199、234)nm附近存在负性CD谱带。D1的ECD谱中在186 nm、228 nm附近存在正性CD谱带,在195nm附近存在负性CD谱带。以上吸收特征可为麻黄碱及其立体异构体绝对构型鉴定提供参考信息。(3)分子轨道成份分析发现,A1、C1分子HOLO轨道主要分布在N(4)原子上,而LUMO轨道主要分布在苯环上。A1、C1理论ECD谱中,峰5的吸收带主要来源于HOMO→LUMO的电子跃迁,即主要由N(4)到苯环的n→π~*荷移跃迁引起。
The electronic structure and electronic circular dichroism (ECD) properties of ephedrine and its stereoisomers were studied by Gaussian 03, SpecDis v1.58, Multiwfn 2.2.1 and Molekel 5.4 software. The results show that: (1) Topological analysis of electron density confirms the existence of bond saddle point between H (7) and N (4) of ephedrine and its stereoisomers. From the saddle point of this bond, (4), indicating the formation of intramolecular hydrogen bonds. (2) The theoretical ECD spectra were obtained. The ECD spectrum of A1 shows a positive CD band around (184,199,229) nm and a negative CD band around 188 nm and 215 nm. The ECD spectrum of B1 has a positive CD band around 184 nm and a negative CD band around 187 m. The ECD spectrum of C1 shows a positive CD band near 185 nm and 222 nm, and a negative CD band near (192, 199, 234) nm. In the ECD spectrum of D1, there is a positive CD band around 186 nm and 228 nm, and a negative CD band around 195 nm. The above absorption characteristics can provide reference information for identifying the absolute configuration of ephedrine and its stereoisomers. (3) Molecular orbital composition analysis shows that HOLO orbitals of A1 and C1 molecules are mainly distributed on N (4) atoms while LUMO orbitals are mainly distributed on the benzene ring. In A1 and C1 theoretical ECD spectra, the absorption band of the peak 5 mainly comes from the electronic transition of HOMO → LUMO, which is mainly caused by the transition of N → π ~ * from N (4) to the benzene ring.