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1.
姜丹  缪振春 《波谱学杂志》2013,30(1):121-130
该文对1,2-取代乙烯衍生物的化学结构的NMR测定方法进行了研究. 结果表明,多频率位移激发双梯度自旋回波1D NOE新方法用于阐明这类化合物的化学结构具有独到之处. 强偶合自旋体系信号的选择性粒子数转移 (SPT)影响可得到有效抑制,NOE信号为吸收型,微小(约0.8%)的NOE信号也可明确测定,重叠复杂的谱峰可分离和辨认,测定顺反异构体不需要标准样品对照,结果准确、可靠. 该文以2-甲氧基-4-(2-苯基-2-环己基氨基甲酰基-乙烯基)-乙酸苯酯为例,阐明1D NOE方法在1,2-取代乙烯衍生物的化学结构和立体化学研究中的应用.  相似文献   

2.
雪灵芝中一新甙——马替诺皂甙的NMR研究   总被引:1,自引:0,他引:1  
从四川雪灵芝中分得一新的Phenylpropanoid Glycoside,Martynoside,经红外,质谱,再采用一维氢谱、碳谱、DEPT谱、旋转坐标NOE差谱和2D远程偶合技术相结合测定该化合物的甙结构.  相似文献   

3.
葛大伦  孔漫 《波谱学杂志》1991,8(3):253-259
本文用核磁共振差谱NOE技术研究了三个小分子化合物的甲氧基构象及几个羟基取代香豆素化合物的结构并得出差谱NOE不能考查螯合OH邻位有无取代基的结论。  相似文献   

4.
8-O-4′型异木脂素立体构型的测定方法   总被引:2,自引:0,他引:2  
原忠  李铣 《波谱学杂志》2003,20(3):307-314
综述了关于8-O-4′型异木脂素的立体化学方面的研究. 总结了测定8-O-4′型异木脂素的相对构型和绝对构型的常用方法. 1H NMR谱是研究C-7 和C-8间相对构型的常用方法, 若H-7的偶合常数较小,在2.7~5.0 Hz范围内,为赤式;若H-7的偶合常数较大,在6.0~8.6 Hz范围内,则为苏式. 结合NOE差谱以及CD谱的测定,或者Mosher's法,可进一步阐明其绝对构型.  相似文献   

5.
差谱NOE的应用   总被引:1,自引:1,他引:0  
本文介绍了核磁共振差谱NOE技术及二个应用实例。  相似文献   

6.
核Overhauser增强(NOE)效应在高场下的化学交换饱和转移中会造成Z谱高场位置的负背景信号,有望成为一种新的磁共振成像(MRI)对比机制.然而,研究指出,NOE信号的发生区域与主要的脂肪信号的频率位置有重叠,因此MRI中观察到的NOE信号有可能混合了脂肪信号.该文通过鸡蛋的模型实验,初步分析了脂肪含量较高的组织内脂肪信号对NOE效应的影响,并通过健康大鼠鼠脑及颅内肿瘤大鼠鼠脑实验,分析了脂肪对脑部NOE对比成像及基于NOE对比成像的疾病诊断的影响.结果表明,脂肪含量较高的组织内脂肪信号会引起伪NOE效应,并影响NOE对比图像的准确性.  相似文献   

7.
合成吲哚生物碱的1H NMR及立体化学   总被引:2,自引:2,他引:0  
报道了5个咔啉和2个吲哚嗪的1H NMK数据.根据它们的COSY谱指定了各质子信号的归属.根据NOESY谱讨论了一些化合物的立体化学.Ⅰb的1-H与3-H存在NOE相关峰,说明1-H与3-CO2Me互为反式.Ⅲ的5'-H与4'-H无NOE相关峰,偶合常数为9.0Hz,它们应为反式.V的1-CHO与2-H有NOE相关峰,说明1-H与2-OH为顺式.由于Ⅱa与Ⅱb有几乎完全相同的NOESY谱.它们的1-H取向只好由经验规律暂定.  相似文献   

8.
姜丹  徐佳 《波谱学杂志》2015,(1):95-104
基于高效镇痛剂双氢埃托啡游离碱,对蒂巴因衍生物的立体化学结构的NMR测定方法进行了研究.结果表明,采用多频率位移选择激发一维NOESY(1D NOESY)和二维NMR(2D NMR)相结合的方法,可有效解决该类化合物1H和13C NMR谱复杂重叠的信号归属困难的问题.同时在阐明溶液构象的基础上,提出采用一维NOE(1D NOE)测定C-7?和?差向异构体的新方法.该方法简单、有效、不受样品浓度影响和杂质信号干扰,结果可靠,不需要标准品对照等优点.该结果有助于此类化合物的立体结构与生物活性关系的研究.  相似文献   

9.
利用二维核磁共振法研究粉防已碱的溶液构象   总被引:2,自引:0,他引:2  
本文利用二维核磁共振的质子NOE谱、四极矩二维谱、异核化学位移相关谱研究了粉防已碱的溶液构象,并确定了五条谱线的归属.  相似文献   

10.
天然孕甾烷-17(20)-烯中C-17位双键的构型对分子的药理性质有重要的影响,但是采用化学位移比较等方法判断其构型存在费时以及区分模糊等缺点. 该文以E-和Z-guggulsterone为模型化合物,利用一维选择性NOE实验来进行天然孕甾烷-17(20)-烯中C-17位双键的构型测定. 由于空间相对位置受到构型影响,选择反转20位的质子时,如果选择性NOE谱中仅能检测到21位甲基氢,表明该化合物为E-构型;如果除了21位甲基氢外,18位甲基氢和12位氢也存在于选择性NOE谱中,则表明该化合物为Z-构型. 实验结果表明该方法具有区分度大,简单快速等优点,可以普遍适用于这些孕甾烷类化合物17位双键构型的确定.  相似文献   

11.
吴祖懿 《波谱学杂志》1986,3(2):147-157
本文提出了予测稠苯芳杂环及其烷基链上质子化学位移的计算方法。 将稠苯芳杂环化合物用凯库勒式表示,计算式为为需考虑的苯环内的乙烯基效应。σmi,ci为各苯环的环流效应。σ1,Hc为各芳杂环的屏蔽效应,对杂环上质子它就是该单独芳杂环上相应质子的δ值,对苯环上质子要将它分解为各结构因素的效应,即:σ1,He=(1/2)d-1δx=y(或σz)+σc-c·σm,H. σx-yσz为杂原子或其基团的屏蔽效应,σc=c为存在于芳杂环中的乙烯基的效应,σm,Hc为芳杂环的环流效应,d为对不同质子所考虑的键数。有取代基时需考虑取代基的效应。计算环上烷基质子的公式为:δ=σp,CH3+ασc,CH3+βσt,CH3+σl,G σl,G为稠苯芳杂环基的某级效应。  相似文献   

12.
Photocurrent measurements on oxidized, single-crystal TiO2 undoped and doped with V, Cr, Mn or Fe were made both before and after exposure to white light from a tungsten lamp; they revealed a band of states centered at 2.0 eV below the conduction-band edge Ec that appears to be the band of surface states active in the photoelectrolysis of water. They also revealed a band of bulk states extending from near the valence-band edge Ev to about 1.9 eV below Ec. The ESR signals from V4+, Cr3+ and Fe3+ ions in oxidized samples and from Mn3+ ions in reduced samples were measured before and after exposure to white and monochromatic light; changes in the ESR signal intensities allow placement of the V4+: d1 level about 2.1 eV below Ec, the Cr3+: d3 level about 2.7 eV belo Ec, the Fe3+ level at or just below the valence band edge Ev which is 3.0 eV below Ec, the Fe2+ level approximately at Ec, the Mn3+ level about 1.9 eV below Ec. Comparison of experiments on oxidized and reduced samples suggests that the bulk states are associated with cation vacancies, and measurements with polarized light gave anisotropies that are qualitatively interpretable with a cation-vacancy model for the oxidized samples.  相似文献   

13.
系统描述了EV共聚物序列中两种结构因素对共聚物主链中亚甲基和次甲基13C NMR化学位移的贡献,将SCS方法与半经验方法结合起来,阐明了常数项δLEδ0的物理意义,提出了以聚乙烯链反式构象化学位移δt为基准计算上述亚甲基和次甲基化学位移的公式:δc=δtniSiPjγj并在此基础上,讨论了聚乙烯,聚丙烯的特殊情况和乙丙共聚物的链结构.  相似文献   

14.
A spin one XY ferromagnet with uniaxial anisotropy has been investigated, using Green's function technique in random phase approximation (RPA). The Green functions associated with the anisotropy energy are treated without decoupling. A set of coupled equations have been obtained to find the critical temperature Tc and (SZ)2 at Tc as function of the uniaxial anisotropy parameter D. Tc and (SZ)2 at Tc are found to increase with D. The results are compared with the earlier results obtained in the Narath type of RPA.  相似文献   

15.
Using a microwave cavity perturbation technique, we have succeeded in observing cyclotron resonances in the layered Perovskite superconductor Sr2RuO4. Three cyclotron masses are deduced, corresponding to mcγ=9.7me, mcβ=5.8me and mc=4.3 me. A comparison between these values and the effective masses deduced from other techniques provides us with a unique means of gauging the role of Coulomb correlations in the title compound.  相似文献   

16.
《Physica A》1995,220(3-4):585-598
An antiferromagnetic equivalent-neighbour Heisenberg interaction Hi between impurity spins is added to the reduced s-d Hamiltonian Hr previously introduced by simplifying the Kondo s-d exchange Hamiltonian HK. Asymptotic mean-field theory is developed for Hr + Hi, in the presence and absence of external magnetic field, and applied to (La1−xCex)Al2 alloys. Specific heat ci(T) and zero-field susceptibility χi(0,T) curves for (La1−xCex)Al2 are depicted. The coupling constants of Hr + Hi and conduction bandwidth are adjusted so that Tc temperatures for x = 0.2, 0.1 are equal to the experimental values. ci(T) exhibits a jump at Tc and is decreasing for T < Tc. χi(0,T) has a first order pole at Tc which corresponds to the maximum of experimental susceptibility and χi(0,0) > 0. These results improve those obtained earlier on the grounds of Hr theory.  相似文献   

17.
Nucleon–nucleon scattering observables are considered in the context of the large Nc limit of QCD for initial states with moderately high momenta (pNc). The scattering is studied in the framework of the time-dependent mean-field approximation. We focus on the dependence of those observables on the spin and isospin of the initial state which may be computed using time-dependent mean-field theory. We show that, up to corrections, all such observables must be invariant under simultaneous spin and isospin flips (i.e., rotations through π/2 in both spin and isospin) acting on either particle. All observables of this class obtained from spin unpolarized measurements must be isospin independent up to 1/Nc corrections. Moreover, it can be shown that the leading correction is of relative order 1/Nc2 rather than 1/Nc.  相似文献   

18.
Superconductivity of compressed, high-purity platinum powder (average grain size 2–3 μm) was found by measurements of resistivity, AC susceptibility and magnetization. The transition temperature into the superconducting state Tc and the critical magnetic field Bc strongly depend on the packing fraction f of the samples: we found 0.62Tc(0)1.38 mK and 6.6Bc(0)67 μT for 0.8f0.5, respectively. The temperature dependence of the critical magnetic fields can be described by Bc(T)=Bc(0)(1−(T/Tc)2). The discussion of these results includes possible explanations for the origin of superconductivity in this new superconducting material.  相似文献   

19.
本文合成了六种含有P-V-W和V-V-W Keggin结构的杂多阴离子,并研究了它们的31P、51V、17O-NMR谱,对于PVxW12-xO40(x+3)-(x=1~4)阴离子,当x=1时,31P和51V-NMR谱只有一条线,并且此线化学位移和pH无关。当x ≥ 2时,谱线数目随着x迅速增加,其原因是几何异构体的数目和类型迅速增加。它们的化学位移δp,和δv。依赖于溶液的酸性和x,即δp,随pH值和x增加而减少,而δv,却随pH和x的增加而增加。最后简短讨论了桥氧上质子化的影响。  相似文献   

20.
过渡金属离子的d-电子特性,使得它们的络合物可以在很多有机合成反应中起催化作用,含三苯磷配体的反式铂氢络合物就是一种稳定的、广泛应用的催化剂[1.2.3.4.]。为此,本工作合成了反式-[PtHXL2],L=PPh3,X=Cl-、Br-、I-、NO3-、NO2-、NCS-六种铂络合物,并测定了其1H-NMR谱。实验获得该络合物系列中,与铂(Ⅱ)相连的质子在高场具有较大的化学位移,即δH=-12~-24ppm和很大的铂-氢偶合常数即Jpt-H=900-1400Hz,以及磷氢偶合常数即Jp-H≈15Hz。此外,还研究了配体对铂-氢的1H化学位移及铂-氢偶合常数;铂-氢键长对铂-氢的1H化学位移的影响,并找出了一定的规律性。从而得到了络合物的顺反异构,键合异构及电子密度分布的有关信息。关于铂络合物的核磁共振研究,虽有过报道[5.6],但配体为三苯膦的反式-[PtH(PPh3)2]系列络合物NMR研究,尚未见报道。  相似文献   

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