Two-dimensional n.m.r. characterization of cycloaliphatic epoxy resins

The cycloaliphatic epoxy resins were studied by various two-dimensional nuclear magnetic resonance (2D n.m.r.) spectroscopies. The ¹³C n.m.r. spectra of the epoxy resins were assigned by using DEPT and 2D INADEQUATE techniques and the ¹H n.m.r. spectra were assigned by using 2D ¹H---¹H and ¹H---¹³C COSY techniques. Complete characterization of the samples synthesized by the oxidation of cyclohexene derivatives not only revealed the existence of the stereochemical isomers resulting from the structural difference of the oxide rings in the samples but also provided the composition ratio of the isomers.     

Al, N, C and H NMR spectra and negative-ion electrospray mass spectra of the 2:1 aluminium(III) complexes of azo dyes derived from anthranilic acid

The ²⁷Al, ¹⁵N, ¹³C and ¹H NMR spectra in DMSO and mass spectra of 2:1 aluminium(III) complexes (1b–4b) derived from anthranilic acid azo coupling products with 4-tert.butylphenol (1a), 2-naphthol (2a) acetoacetanilide (3a) 3-methyl-1-phenylpyrazol-5-one (4a) were measured and analysed. It was found that the aluminium atom was six-coordinated, being bound to two oxygens and the nitrogen originating from anthranilic acid.     

Influence of the SiO2/Al2O3 ratio on the synthesis and physicochemical characteristics of levyne-type zeolite

Levyne-type zeolites were synthesized from gels of initial compositions 4.5Na₂O-6MeQI-xAl₂O₃ 30SiO₂-500H₂O, with MeQ = methylquinuclidinium and 0.6 ≤ x ≥ 3 at 150 ≤ t ≥ 190 °C. The ²⁹Si NMR spectra show the presence of two crystallographically different sites in the structure. The ²⁷Al NMR spectra also suggest the presence of two different tetrahedral Al atoms incorporated in the structure. A rather high amount of defect groups SiOM and Si(OM)₂ with M = MeQ, Na and/or H are present in the precursor samples. The Si(OM)₂ groups are eliminated during calcination, and a certain amount of SiOM still persists after calcination. The combined ¹³C NMR and thermal analysis data allowed one to interpret the nature of the two different types of MeQ⁺ ions occluded in the levyne channels.     

Quantitative C n.m.r. spectroscopy of a coal-derived oil and the assignment of chemical shifts

The conditions necessary for the recording of quantitative ¹³C nuclear magnetic resonance spectra of the hexane-soluble oil separated from a coal hydrogenation product have been investigated. Measured values of T₁ for different signals in the spectrum were less than 1 s, and altering the pulse-repetition time beyond 2–4 s had little effect on carbon aromaticities. The nuclear Overhauser effect was suppressed by gating the proton decoupling. Assignments of chemical shifts for various signals in the spectrum of the oil were made by reference to literature spectra of polyaromatic substances and their derivatives. Determinations of different structural carbon types were internally consistent.     

Evaluation of the aromatic structure of coal tar pitch by solid and solution state n.m.r.

Rapid magic angle spinning has been used to obtain sideband-free high field ¹³C n.m.r. spectra of coal tar pitches in the solid state. However, the unfavourable cross-polarization and ¹H relaxation characteristics make it difficult to accurately estimate concentrations of quaternary aromatic carbon using the dipolar dephasing method. The concentrations of bridgehead aromatic carbon in the whole pitch and toluene-insoluble fraction investigated were deduced using a combination of solid and solution state n.m.r. and elemental analyses.     

C-tracer study of the Fischer–Tropsch synthesis: another interpretation

The ¹³C-tracer results from the introduction of ¹³C₂H₄ into syngas prior to conversion with a rhodium catalyst have been used to support a surface vinyl mechanism for Fischer–Tropsch synthesis. The results were first interpreted by a mechanism that involved a decrease in ¹³C species on the surface as the carbon number increased. This model is shown to be incorrect. Considering only the ¹³C-labeled products, the data are consistent with earlier tracer studies showing that the added ¹³C₂H₄ initiates chains.     

Hydrocarbon structural group analysis of Athabasca asphaltene and its g.p.c. fractions by C n.m.r.

Asphaltene from the Athabasca oil sand bitumen separated according to molecular weight by gel permeation chromatography was examined by high resolution solution-state ¹³C and ¹H and solid state ¹³C n.m.r. Integration of the inverse gated decoupled solution state and CP/MAS ¹³C n.m.r. spectra gave the aromaticity of each fraction as well as the relative number of carbon atoms responsible for well resolved signals in the aliphatic portion of the spectra. A two-pulse spin-echo ¹³C n.m.r. sequence in the solution state, and dipolar dephasing in the solid state, permitted the assignment of each aliphatic carbon signal to a methyl, methylene, or methine carbon; no quaternary aliphatic carbons were observed. These signals show that the aromatic core of the asphaltene is surrounded by alkyl chains with a mean length of 7.7 for the lowest molecular weight fraction (MW 1200), increasing to 12 for the highest MW fraction (MW 16900). Aromaticity of the fractions obtained from solution spectra ranged from 34 to 48%, the highest aromaticity being associated with the lowest molecular weight asphaltenes. In the solid state, the aromaticity ranged from 31 to 42 %. The degree of branching ranged from 0.5 per chain for the low MW asphaltene to 1.0 for the high MW fraction. The highest naphthenic carbon content was found in the high MW fractions; the 1200 MW fraction appeared to be nearly devoid of such carbon, this fraction having a much higher aromaticity than the second-lowest MW fraction.     

Dielectric and C n.m.r. studies of various stereostructural forms of poly(N-vinyl carbazole)

Three different stereostructural forms of poly(N-vinyl carbazole) (PVK) have been prepared using cationic (AlCl₃ and BF₃(CH₂CH₃)₂O) and radical (azobisisobutyronitrile) initiators. The dipole moment per repeat unit of PVK has been determined and correlated with ¹³C n.m.r. spectra of the methine and methylene carbon absorptions for fractions of PVK in solution in 1,4-dioxan. The dielectric data for cationically prepared PVK appear to indicate a random coil configuration or possibly a rod-like structure in which the dipole moment vectors of the carbazole groups are randomly oriented but remain approximately perpendicular to the long axis of the molecule. For each type of PVK examined the repeat unit dipole moment was observed to be independent of molecular weight over the range 10⁴–10⁷ and insensitive to polydispersity.     

EPR and optical spectra of Cu2 in dioptase

EPR and optical absorption studies of Dioptase have been carried out at room and low temperatures. The observed, absorption bands have been attributed to Cu²⁺ ion in C_4V symmetry. From the g-values, the ground state of Cu²⁺ is found to be ²B₁. The octahedral and tetragonal field parameters and the spin-orbit reduction parameters have been evaluated. The NIR and IR spectra have also been reported.     

水溶性弛豫试剂在醇、酸、胺体系中的定量研究

在核磁共振实验中,13C核弛豫慢,利用核磁共振13C谱对应用体系中的碳核进行定量分析需要耗费大量的实验时间,通常需要在体系中加入顺磁性弛豫试剂,可以有效提高'3C核的弛豫速率,缩短实验时间.开发了EDTA-Cu作为弛豫试剂,分别应用于不同类型的水溶性样品,研究结果表明EDTA-Cu配合物浓度为0.03～0.04mol/...     

Evaluation of a delayed coking process by H and C n.m.r. spectroscopy: 2. Detailed interpretation of liquid n.m.r. spectra

The ¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectra of a delayed coking feedstock and products, presented in a previous paper, are analysed here in detail by matching results from inspection of both nuclei. The conventional spectra of whole samples are used in combination with elemental analysis data, and substantial agreement is obtained. Differences are explored to yield valuable information. Interpretation of some band assignments is modified to account for new results. This approach results in a detailed quantitative estimation of a few key structures that contain the main functional groups that characterize these petroleum fractions.     

宁东红石湾煤大分子模型构建及量子化学计算

使用工业分析、元素分析、固体核磁（¹³C NMR）、X射线光电子能谱（XPS）、傅里叶变换红外光谱（FT-IR）对宁东红石湾（HSW）煤样进行表征,获得煤样中元素赋存的种类、价态、化学键环境等物质微观结构的关键参数。结果表明HSW煤结构以芳香族为主,占75.96%,桥接芳碳与周碳比为0.315,可知其结构中以萘为主,苯和蒽为辅。氧原子主要以醚氧基（C-O）、羰基（C=O）和羧基（-COO）的形式存在,其中C-O占53.57%。氮原子以吡啶和吡咯的形式存在。苯环的连接方式以三、四取代为主,分别占47.77%、32.97%,脂肪族中环烷烃或脂肪烃-CH₃占优势。确定HSW煤的分子式为C₂₂₁H₁₄₈O₂₈N₂,分子量为3142.32。在此基础上结合计算机辅助实现了二维和三维大分子模型构筑。应用量子化学计算对HSW煤大分子模型进行了优化及核磁共振、红外光谱模拟,验证了所建模型的合理性。最终实现了HSW煤的微观分子结构的实验与量子化学描述。     

均三嗪衍生物比色识别Cu2+及荧光识别Zn2+

以对氨基苯腈、邻叔丁基苯酚和3,5-二叔丁基水杨醛为原料合成了两种含有均三嗪对称结构的离子探针1和2,通过核磁共振氢谱、核磁共振碳谱、红外、质谱对合成产物进行表征,确认其结构。利用紫外吸收光谱和荧光光谱两种手段分别考察了探针1和探针2在N,N-二甲基甲酰胺（DMF）溶液中对金属离子（Cr³⁺、Mn²⁺、Fe³⁺、Co²⁺、Ni²⁺、Cu²⁺、Zn²⁺、Cd²⁺、Hg²⁺）的识别性能,通过核磁共振氢谱对探针1与Zn²⁺的识别机理进行研究。结果表明,两种探针热稳定性强,探针1溶液中加入Zn²⁺会引起荧光强度的显著增强,抗干扰性强,是一种高选择性识别Zn²⁺的荧光增强型探针;探针2中加入Cu²⁺后溶液由无色变成黄色,紫外光谱长波长处出现新吸收峰,是一种可裸眼识别的、高效的紫外Cu²⁺探针。     

Water mediated modification of structure and physical chemical properties of nanocarbons

Considerable amount of water incapsulated in native shungite carbon (ShC) and its amphiphilic properties are originated from fullerene-like structure. We report on the study of ShC and its stable aqueous dispersion by high-resolution solid state ¹³С and ¹Н MAS NMR, and time-of-flight (TOF) mass spectrometry. ¹³С NMR spectrum changes substantially as ShC was transformed into aqueous dispersion: a narrow sp²-carbon signal (at 116 ppm) attributed to the basic structural unit (BSU) in the form of bowls is observed. Distance from carbon atoms in BSU to hydrogen atoms of water was estimated at  0.8 nm using cross-polarization technique. ¹H solid state NMR spectrum consists of two peaks at 0.40 and 3.16 ppm. They were assumed to be related to water complexes on BSU (0.40 ppm) and to adsorbed water (3.16 ppm). TOF mass spectra of the ShC aqueous dispersion showed maximum intensity at  284 m/z corresponding to the dominant structure of ShC.     

Electrochemical and spectroscopic properties of 1:2 Ni complexes of 1,3-substitued (CH3, OCH3) phenyl-5-phenylformazans

In this study, new 1:2 nickel complexes of 1-[o-, m-, p-(methyl, metoxyphenyl)]-3-(p-metoxyphenyl)-5-phenylformazans were synthesized. Their structures were elucidated and spectral behaviors were investigated with the use of elemental analysis, GC–mass, ¹H NMR, ¹³C NMR, IR, and UV–vis spectra. The redox characteristics of these compounds have been investigated in nonaqueous dimethylsulfoxide at platinum and ultramicro platinum (10 μm) electrodes. Through controlled potential electrolysis, the oxidation products of each class of compounds can be separated and identified. The oxidation mechanism is suggested and it is proved. It was observed the oxidation mechanism take place in a single step two-electron or one-electron transfer to a disproportionation or dimerization reactions following the radical formation step. Eventually the relation between their absorption properties and electrochemical properties was examined.     

Development of structural characterization and physicochemical behaviour of triphenylamine blocks

A novel multitriphenylamine substituted derivatives, possessing the respective photochromic groups were synthesized by Stille cross-coupling methodology. The hyperbranched structures have been characterized by ¹H NMR, ¹³C NMR. Obtained structures show good stability in common organic solvents such as CHCl₃, toluene and CH₂Cl₂ and exhibit excellent thermal stability. Electrochemical results and theoretical calculation suggest that oxidation and reduction start from the side of amine and branching five member heterocycle ring moieties, respectively.     

异辛基乙二胺-酰基丙氨酸型质子化离子液体的分子间氢键相互作用

利用密度泛函理论M06-2X/6-311G(d,p)方法及基组条件下,对异辛基乙二胺-酰基丙氨酸型质子化离子液体[HEtHex]⁺[Acylala]^-(Acyl =butanoyl, hexanoyl)的几何构型进行了优化,分别得到了5种较稳定构型S1~S5。结果显示,[HEtHex][Butlala]及[HEtHex][Hexlala]的基组重叠误差校正后的分子间相互作用能(ΔE₀^BSSE)均在-136.14~-117.26 kcal·mol^-1（1 kcal·mol^-1=4.182 kJ·mol^-1）范围内,其中伯胺质子化构型(S1~S3)的相互作用能(-136.14~-127.01 kcal·mol^-1)大于仲胺质子化构型(S4~S5)(-119.03~-117.26 kcal·mol^-1)。由于[HEtHex][Acylala]阴阳离子间发生了质子转移而形成了较强的O—H…N型氢键,引起[HEtHex]⁺中N—H振动频率消失,并在2400~2815 cm^-1处出现了较强的O—H的伸缩振动,即以分子与分子间的作用力键合。自然键轨道及分子中原子理论计算结果显示,[HEtHex][Acylala]间所形成氢键的稳定化能主要来源于[EtHex]分子中胺基N原子的孤对电子lp(N)与[Acylala]分子中羧基的反键轨道σ*(O—H)间的相互作用。并且分子间氢键能及二阶微扰能分别在18.69 ~ 24.19 kcal·mol^-1及43.58 ~57.58 kcal?mol^-1范围内,属于较强类型氢键作用。     

CHAINGROWTH IN FISCHER-TROPSCH CATALYSIS, AS OBSERVED WITH TRANSIENT-KINETIC METHODS

An abrupt change in the reaction ambient from ¹²CO/H₂ to ¹³CO/H₂ leads to a gradual ingrowth of ¹³C in hydrocarbon chains. From the rate of ¹³C ingrowth we calculate C—C bonds to form on a time scale varying from ≤1 s (ruthenium) to ≥10s (cobalt).     

High resolution solid state C n.m.r. of Canadian peats

Peat samples from three locations in Quebec, Canada, were characterized by ¹³C CP/MAS n.m.r. spectroscopy. The n.m.r. analysis indicates that the peats contain a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes and resins. Integration of specific regions of the spectra can give semi-quantitative estimates of some of these plant components and, in limited cases, information about the degree of decomposition can be obtained from the ¹³C CP/MAS n.m.r. spectrum. Dipolar dephasing experiments and difference spectroscopy were found to be valuable techniques for spectra assignments and enhancement of compositional differences.     

Use of isotopic labeling for mechanistic studies of the methanol-to-hydrocarbons reaction. Methylation of toluene with methanol over H-ZSM-5, H-mordenite and H-beta

Methylation of toluene (in one case benzene) with methanol has been investigated over four different zeolites: Small and large crystal ZSM-5, dealuminated mordenite and zeolite beta. The feed ratio methanol/arene was varied over a wide range, mostly >1, using nitrogen or helium as carrier gas. A rather high space velocity was employed (WHSV (methanol + arene): 5–35 h⁻¹). The reaction temperature was 350°C or 375°C. A parallel set of experiments was performed using ¹³C methanol (99% ¹³C). The products were analyzed by on-line gas chromatography using a GC–MS system allowing determination of isotopic composition of the more important products, i.e., ethene, propene and the arenes when ¹³C methanol was employed, otherwise a FID was used. The goal was to obtain mechanistic information, and no attempt has been made to optimize for any particular reaction product.

The experiments showed that ethene and propene were isotopically mixed, containing 50–75% ¹³C. The 25–50% ¹²C atoms coming from the reactant arene. Over all catalysts the arene was, when fed alone, essentially inert with 0.5% or less conversion, giving neither ethene nor propene in measurable quantities. The isotopic distribution in ethene was indistinguishable from a random distribution. Propene, although being close to, displayed some deviation from randomness. The ¹²C/¹³C isotopic ratio in propene was equal to that in ethene, and they both varied with the methanol/arene ratio in the feed, but much less so than the variation in feed composition.

The results support a pool mechanism where the catalytic activity for converting methanol to hydrocarbons is connected with the presence of adsorbates in the zeolite cavities which add methanol and split off product molecules, notably ethene and propene. Formation of ethene by reaction between C₁ species is at best a minor reaction. While formation of propene may take place by a homologation/cracking mechanism, this route was of minor importance here.

Polymethylbenzenes which were formed in many cases displayed a pronounced isotopic scrambling, containing up to six ¹³C atoms in the benzene ring. Molecules with fewer ¹³C atoms than the number of added methyl groups were also identified.