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<正> 核磁共振二维谱是研究高聚物分子结构的有力工具.有时一张谱图,就能得到高聚物序列结构或共聚物构型的直接证据.对高聚物结构分析有重要意义.自1983年Brown首次报道聚氯乙烯的二维J谱以来.美国Macromolecules等杂志竟相报道各种聚合物的二维谱图.目前已经报道过的聚合物核磁共振二维谱有二维J谱、~(19)F-~1H异核相关谱、~(13)C-~1H异核相关谱、~1H COSY谱、~(19)F COSY谱、NOESY 相似文献
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A heteronuclear compound, K2[Co(Dipc)2]·7H2O (Dipc=pyridine-2,6-dicarboxylic acid) has been synthe- sized and characterized by IR, elemental analysis, and X-ray diffraction. Crystal data: orthorhombic system with space group Pnna and unite cell parameters: a=2.0645(3)nm, b=1.3484(2)nm, c=0.8204(1)nm; V=2.2838(6)nm3, Z=4, Dcald=1.726 g·cm-3, μ=1.193 mm-1, F(000)=1212, Gof=1.045, Δρ=339~-348 e·nm-3, the final R is 0.0295. In the molecule of the complex, Co(Ⅱ) ion is six-coordinate to form a dis-torted octahedron. The N atom and the carboxyl group of pyridine-2,6-dicarboxylic acid are coordinated with the central ions. One of the carboxyl groups of the pyridine-2,6-dicarboxylic acid connect K(Ⅰ) and Co(Ⅱ). The com- pound possesses approximate C2 symmetry. The compounds form a three-dimensional network of infinite length connection with crystal waters, potassium ions and hydrogen bonds. The result of kinetics of thermal decomposition indicated that the compound decomposition takes place in two steps. CCDC: 207078. 相似文献
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利用过渡金属锰盐与稀土盐水热合成了杂核化合物{[MnSm2(INAIP)4(H2O)4]·2H2O}n (1)和同核{[Sm(INAIP)(HINAIP)]·2H2O}n (2)(INAIP=异烟酰胺吡啶基异酞酸根),并对其进行了元素分析、IR及X-射线衍射法表征.晶体结构研究表明:配合物1属于三斜晶系,P1 空间群.晶胞参数:a=1.018 8(5) nm,b=1.083 86(6) nm,c=1.387 21(8) nm,V=1.475(14) nm3,Z=1,Dc=1.802 g·cm-3,μ=2.271 mm-1,F(000)=793,Rint=0.010 5,R1=0.051 2,wR2=0.131 9.配合物2属于单斜晶系,P21/c空间群.晶胞参数:a=1.343 05(18)nm,b=1.376 5(17) nm,c=1.62408(15) nm,V=2.7028(6) nm3,Z=4,Dc=1.861 g·cm-3,μ=2.251 mm-1,F(000)=1 500,Rint=0.051 4,R1=0.032 2,wR2=0.088 7.配合物1是由配体INAIP连接稀土钐离子形成二维层状结构,该二维层通过Mn-O和Mn-N键连接成三维非贯穿网络结构.而配合物2是由配体INAIP连接稀土钐离子形成二维双层状结构,该二维层通过氢键连接成三维网络结构.配合物1失去水分子后具有稳定微孔结构,对二氧化碳具有一定的吸附,而对氮气没有吸附作用.此外,配合物1和2具有典型的稀土钐离子红色荧光性能. 相似文献
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利用过渡金属锰盐与稀土盐水热合成了杂核化合物{[MnSm2(INAIP)4(H2O)4]·2H2O}n(1)和同核{[Sm(INAIP)(HINAIP)]·2H2O}n(2)(INAIP=异烟酰胺吡啶基异酞酸根),并对其进行了元素分析、IR及X-射线衍射法表征。晶体结构研究表明:配合物1属于三斜晶系,P1空间群。晶胞参数:a=1.0188(5)nm,b=1.08386(6)nm,c=1.38721(8)nm,V=1.475(14)nm3,Z=1,Dc=1.802g·cm-3,μ=2.271mm-1,F(000)=793,Rint=0.0105,R1=0.0512,wR2=0.1319。配合物2属于单斜晶系,P21/c空间群。晶胞参数:a=1.34305(18)nm,b=1.3765(17)nm,c=1.62408(15)nm,V=2.7028(6)nm3,Z=4,Dc=1.861g·cm-3,μ=2.251mm-1,F(000)=1500,Rint=0.0514,R1=0.0322,wR2=0.0887。配合物1是由配体INAIP连接稀土钐离子形成二维层状结构,该二维层通过Mn-O和Mn-N键连接成三维非贯穿网络结构。而配合物2是由配体INAIP连接稀土钐离子形成二维双层状结构,该二维层通过氢键连接成三维网络结构。配合物1失去水分子后具有稳定微孔结构,对二氧化碳具有一定的吸附,而对氮气没有吸附作用。此外,配合物1和2具有典型的稀土钐离子红色荧光性能。 相似文献
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Bischler-Napieralski反应是合成3,4-二氢异喹啉的经典方法。通过文献调研,对其机理、影响因素、拓展研究及应用进行综述,发现Bischler-Napieralski反应已被广泛运用于医药、化工等重要中间体的合成,但三氯氧磷、五氧化二磷等脱水剂的使用仍较频繁。 相似文献
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The γ-substituted β-diketonate 2,4-dioxo-3-pentyl 4-[4-(n-octyloxy)cinnamoyl]oxybenzoate 1 and its pyrazole and isoxazole derivatives (2 and 3 respectively) have been synthesized and characterized by the spectroscopic methods and elemental analysis. The mesogenic properties of these compounds have been studied by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). A monotropic nematic mesophase was observed for the β-diketonate 1, in contrast, the pyrazole 2 displays an enantiotropic smectic A and isoxazole 3 exhibits an enantiotropic nematic mesophase. The relationship between the structure and liquid crystalline properties has also been discussed. 相似文献
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Rundlöf T Eriksson L Widmalm G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(8):1750-1758
Proton-proton cross-relaxation rates have been measured for the trisaccharide beta-D-Glcp-(l --> 2)[beta-D-Glcp-(1 --> 3)]alpha-D-Glcp-OMe in D2O as well as in D2O/[D6]DMSO 7:3 solution at 30 degrees C by means of one-dimensional NMR pulsed field gradient 1H,1H NOESY and TROESY experiments. Interatomic distances for the trisaccharide in D2O were calculated from the cross-relaxation rates for two intraresidue and three interglycosidic proton pairs, using the isolated spin-pair approximation. In the solvent mixture one intraresidue and three interglycosidic distances were derived without the use of a specific molecular model. In this case the distances were calculated from the cross-relaxation rates in combination with "model-free" motional parameters previously derived from 13C relaxation measurements. The proton-proton distances for interglycosidic pairs were compared with those averaged from Metropolis Monte Carlo and Langevin Dynamics simulations with the HSEA, PARM22, and CHEAT95 force fields. The crystal structure of the trisaccharide was solved by analysis of X-ray data. Interresidue proton pairs from the crystal structure and those observed by NMR experiments were similar. However, the corresponding proton-proton distances generated by computer simulations were longer. For the (1 --> 2) linkage the glycosidic torsion angles of the crystal structure were found in a region of conformational space populated by all three force fields, whereas for the (1 --> 3) linkage they occupied a region of low population density, as seen from the simulations. 相似文献
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A novel strategy for NMR analysis of mixtures of oleanolic and ursolic acids that occur in natural products is described. These important phytochemicals have similar structure and their discrimination and quantification is rather difficult. We report herein the combined use of proton-carbon heteronuclear single-quantum coherence (1H-13C HSQC) and proton-carbon heteronuclear multiple-bond correlation (1H-13C HMBC) NMR spectroscopy, in the identification and quantitation of oleanolic acid (OA) and ursolic acid (UA)in plant extracts of the Lamiaceae and Oleaceae family. The combination of 1H-13C HSQC and 1H-13C HMBC techniques allows the connection of the proton and carbon-13 spins across the molecular backbone resulting in the identification and, thus, discrimination of oleanolic and ursolic acid without resorting to physicochemical separation of the components. The quantitative results provided by 2D 1H-13C HSQC NMR data were obtained within a short period of time (∼14 min) and are in excellent agreement with those obtained by HPLC, which support the efficiency of the suggested methodology. 相似文献
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Intermolecular cross-relaxation rates between solute and solvent were measured by {1H} 19F nuclear magnetic resonance experiments in aqueous molecular solutions of ammonium perfluoro-octanoate and sodium trifluoroacetate. The experiments performed at three different magnetic fields provide frequency-dependent cross-relaxation rates which demonstrate clearly the lack of extreme narrowing for nuclear spin relaxation by diffusionally modulated intermolecular interactions. Supplemented by suitable intramolecular cross-relaxation, longitudinal relaxation, and self-diffusion data, the obtained cross-relaxation rates are evaluated within the framework of recent relaxation models and provide information about the hydrophobic hydration. In particular, water dynamics around the trifluoromethyl group in ammonium perfluoro-octanoate are more retarded than that in the smaller trifluoroacetate. 相似文献
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Using double-resonance conditions, in which the Larmor frequency of a spin-1/2 nucleus is matched to one of the nuclear quadrupole resonance frequencies of a spin-1 nucleus, the authors demonstrate increased cross relaxation between the two nuclear spin species. They calculate the cross-relaxation rate using the motionally averaged heterogeneous dipole Hamiltonian as a perturbation to the combined quadrupole and Zeeman Hamiltonians. Using this cross-relaxation rate, in addition to hydrogen and nitrogen autorelaxation rates, expressions governing spin-1/2 and spin-1 spin-lattice relaxation are determined. With ammonium nitrate, containing nitrogen (spin-1) and hydrogen (spin-1/2), increased nitrogen signal and spin-lattice relaxation are demonstrated, using fields less than 120 G. The cross-relaxation rate is also measured and an overall signal/noise improvement by a factor of 2.3+/-0.1 is attained. 相似文献
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Suresh Mani H. H. Winter M. Silverstein M. Narkis 《Colloid and polymer science》1989,267(11):1002-1006
Emulsion polymerized interpenetratingpolymer networks (IPN) of polyacrylate and polystyrene exhibit a power law relaxation over a wide frequency range. The response of the material to oscillatory shear, step sheaf strain and a constant stress can be described with a two parameter constitutive equation. The power law behavior was previously found in polymers at their critical state where molecular motions were correlated over large distances without intrinsic size or time scale.The effect of composition and crosslink density on the behavior of the material is studied. The behavior might be explained with the granular structure of the material. 相似文献
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Measurements of the enhancement, by various electrolytes, of the spin-lattice relaxation time of carbon-13 at different locations in a number of amino acids are reported. Spin-lattice relaxation times T1 of all the carbons in amino acids generally tend to decrease with increase in the concentration of electrolytes, the largest effects often being observed for the charged carboxylate groups of the amino acids. Carboxylic carbons in amino acids are the sensitive 'acceptor' of the 13C spin-lattice relaxation accelerating effects offered by electrolytes, and the 13C spin-lattice relaxation accelerating ability of electrolytes decreases in the order Mg(ClO4)2 > MgCl2 > CaCl2 > NaCl > KCl > LiClO4 > NaOH. The mechanisms of the observed phenomena are discussed in terms of intermolecular interaction, paramagnetic impurities in electrolytes and other mechanisms; large contributions of intermolecular interactions with electrolytes are present on complex formation between amino acids and metal ions and the incoming 'unsaturation' of the primary solvation shell of cations with the increase in electrolyte concentration. 相似文献
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D. Olčák V. Hronský P. Vrábel I. Chodák P. Alexy 《International Journal of Polymer Analysis and Characterization》2015,20(5):396-405
Single-pulse 13C NMR spectra and spin-lattice relaxation times T1(1H), detected indirectly via 13C carbons, and T1(13C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the 13C NMR lines and proton spin-lattice relaxation times T1(1H). The spin-lattice relaxation times T1(13C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study. 相似文献
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Purity analysis of hydrogen cyanide, cyanogen chloride and phosgene by quantitative (13)C NMR spectroscopy 总被引:1,自引:0,他引:1
Hydrogen cyanide, cyanogen chloride and phosgene are produced in tremendously large quantities today by the chemical industry. The compounds are also particularly attractive to foreign states and terrorists seeking an inexpensive mass-destruction capability. Along with contemporary warfare agents, therefore, the US Army evaluates protective equipment used by warfighters and domestic emergency responders against the compounds, and requires their certification at > or = 95 carbon atom % before use. We have investigated the (13)C spin-lattice relaxation behavior of the compounds to develop a quantitative NMR method for characterizing chemical lots supplied to the Army. Behavior was assessed at 75 and 126 MHz for temperatures between 5 and 15 degrees C to hold the compounds in their liquid states, dramatically improving detection sensitivity. T(1) values for cyanogen chloride and phosgene were somewhat comparable, ranging between 20 and 31 s. Hydrogen cyanide values were significantly shorter at 10-18 s, most likely because of a (1)H--(13)C dipolar contribution to relaxation not possible for the other compounds. The T(1) measurements were used to derive relaxation delays for collecting the quantitative (13)C data sets. At 126 MHz, only a single data acquisition with a cryogenic probehead gave a signal-to-noise ratio exceeding that necessary for certifying the compounds at > or = 95 carbon atom % and 99% confidence. Data acquired at 75 MHz with a conventional probehead, however, required > or = 5 acquisitions to reach this certifying signal-to-noise ratio for phosgene, and >/= 12 acquisitions were required for the other compounds under these same conditions. In terms of accuracy and execution time, the NMR method rivals typical chromatographic methods. 相似文献
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Steven T. Parslow Najlaa K. Almazrouei Michael I. Newton Elizabeth R. Dye Robert H. Morris 《Magnetic resonance in chemistry : MRC》2019,57(9):695-699
Moisture content of foodstuffs are typically assessed by Titration or Near Infrared Spectroscopy, which are labour-intensive as a manual measurement or costly when automated. Magnetic resonance offers a method for moisture evaluation but is also normally costly. In this work, we revisit Look and Locker's “Tone Burst” experiment with a marginal oscillator to evaluate moisture content of powdered–skimmed milk subjected to increased humidity. We refer to this technique as the Transient Effect Determination of Spin–Lattice (TEDSpiL) relaxation times. Moisture content in the samples ranged from 0–12% as determined from the weight gained by the dry powder when re-suspended in water to reach a concentration of 40% w/v. The relaxation properties of re-hydrated samples were measured with a CW NMR sensor. Solutions made up from powders with a higher retained moisture content provided lower measured relaxation values providing a method of measuring the moisture content of the powder. This technique provides a moisture measurement in under 5∼s compared with several minutes for the equivalent pulsed method using low-field hardware. 相似文献