1H MAS, 13C CP/MAS, and 2H NMR spectra studies of piperidinium {\emph{p}}-chlorobenzoate

Anomalous H/D isotope effects were detected in the ¹H MAS NMR spectra of piperidinium p-chlorobenzoate (C₅H₁₀NH $_{2}{^{+}}\cdot $ ClC₆H₄COO^???) upon deuterium substitution of hydrogen atoms which form two kinds of N-H?O H-bonds in the crystal; in contrast to these spectra, only slight chemical shifts were recorded in ¹³C CP/MAS NMR spectra. ²H NMR spectrum of the deuterated sample show quadrupole coupling constants of 148 and 108 kHz, and reveal that there are a few motions contributing to the electric-field modulation of the ²H nucleus. The ¹H MAS NMR spectra of piperidinium p-chlrobenzoate-d ₁₆ (C₅D₁₀ND $_{2}{^{+}}\cdot $ ClC₆D₄COO^???) and -d ₁₄ (C₅D₁₀NH $_{2}{^{+}}\cdot $ ClC₆D₄COO^???) revealed that the change in the envelope is caused by chemical shifts of each signal upon deuteration. Calculations based on the density-functional-theory showed that the N-H distance along the crystallographic a-axis mainly contributes to the anomalous isotope effects on ¹H MAS NMR envelopes.     

13C MAS NMR investigations of alkali doped C60

Results of¹³C MAS NMR measurements of the Rb _x C₆₀ system (x=2.75, 3, 4, 6) and the A₆C₆₀ compounds (A=K, Rb, Cs) are presented. Special attention was paid to sample preparation in order to suppress effects of impurities and lattice defects due to imperfect C₆₀ starting material. The¹³C MAS NMR measurements of the Rb _x C₆₀ system demonstrate the usefulness of this method to reveal valuable information about its phase diagram. The existence of underdoped Rb₃C₆₀ is proved. Well resolved lines in all investigated A₆C₆₀ compounds confirm the orientational order of the C₆₀ ions. An assignment of the signals to the three magnetically inequivalent carbon atom positions in the crystal structure is proposed.     

吉士脱酮的1H及13C NMR研究

Gestodene是避孕药物18甲基炔诺酮的衍生物,动物实验表明它的孕激素活性为18甲基炔诺酮的3~5倍.本文采用各种2D NMR技术,包括:¹H-¹H COSY,¹H-¹³C COSY和HMBC等,归属了它的¹H和¹³C的谱线,并得到了有关质子间的偶合常数.     

13C CP MAS NMR and GIAO-CHF calculations of coumarins

13C cross-polarization magic-angle spinning NMR spectra were recorded for a series of solid coumarins. Ab initio calculations of shielding constants were performed with the use of GIAO-CHF method. The combined CPMAS NMR and theoretical approach was successful in characterizing solid-state conformations of coumarins; a relationship sigma (ppm) = -1.032 xdelta + 205.28 (R(2) = 0.9845) can be used to obtain structural information for coumarins, for which solid-state NMR or crystal structure data are not available.     

Experimental method for low-temperature reaction studies in sealed samples by 13C CP/MAS NMR

A new, simple, and inexpensive technique is presented for monitoring high-resolution solid-state NMR of ¹³C at temperatures ranging between 85 and 450 K. In this procedure, the reaction conditions are controlled by preparing samples at 77 K in 5 mm NMR tubes, while attached to a vacuum system. The NMR tubes are prefitted with a rotor for spinning. After preparation, the samples are sealed, transferred to the double-resonance MAS NMR probe, and analyzed, all while the sample temperature is maintained as low as 85 K. The spinning rates vary from 3.0 kHz at 85 K to 5.2 kHz at 300 K using nitrogen drive gas. Probe design and performance, sample-preparation procedure, and details of the low-temperature experiment are described. In general, the technique may be applied in studies of low-temperature reaction mechanisms and kinetics. ¹³C CP/MAS spectra of ethylene adsorbed on silica-supported ruthenium catalyst are presented to illustrate its performance and possible application.     

1H and 13C NMR Determination of 1-Naphtyl-Polymethoxylated Diphenylwiethanes

The complete structural analysis of 1-[(4-methoxyphenyl)-(3,4,5-trimethoxyphe- nyl)methyl]naphtalene 5a and 1-[(2,5-dimethoxyphenyl)-(3,4,5-trimethoxyphenyl) methyljnaphtalene 5b, prepared by alkylation of 1-[chloro-(3,4,5-trimethoxyphenyl) methyl]naphtalene without by-products such as benzofluorene 2, may be accurately determined by ¹H, ¹³C NMR and 2D NMR analysis.     

MAS NMR studies of carbon-13 spin exchange in durene

One- (1-D) and two-dimensional (2-D) carbon-13 NMR exchange measurements in powder samples of isotopically normal durene under magic angle spinning (MAS) are reported. The experiments include rotor synchronized 2-D exchange (RS2DE), 1-D magnetization transfer (MT) and time reverse ODESSA (tr-ODESSA). The latter two experiments were performed as a function of several external parameters, including proton decoupling field during mixing time, sample spinning rate and partly, of temperature. The effects of these parameters on the spin exchange induced by spin diffusion and by chemical, or physical exchange, is discussed. Spin exchange between all types of carbons in the durene molecules occurs on the time scale of seconds. From the dependence of the spin exchange rate on the external parameters it is concluded that the process is dominated by spin diffusion. On the basis of these results an upper limit of 10(-16) cm2 s(-1) can be set for the self-diffusion constant in crystalline durene.     

1H AND 13C NMR Assignments of Artheethers

The ¹H and ¹³C nmr assignments for all hydrogen and carbon atoms were made for β and α arteethers (5 and 6) based on chemical shift theory and 2D-nmr techniques (COSY and HETCOR).     

13C cross-polarization MAS NMR study of some steroidal sapogenins

Cross-polarization (CP) magic angle spinning (MAS) solid-state 13C NMR spectra of five steroidal sapogenins: tigogenin ((25R)-5alpha-spirostan-3beta-ol), hecogenin (3beta-hydroxy-(25R)-5alpha-spirostan-12-one), diosgenin ((delta5-(25R)-5alpha-spirosten-3beta-ol), sarsasapogenin ((25S)-55beta-spirostan-3beta-ol), and smilagenin ((25R)-5beta-spirostan-3beta-ol) were recorded. The solid-state chemical shifts are almost the same as for solution, which indicate that confirmations of sapogenins are similar in both phases. The doubling of some resonances in the spectra of solid diosgenin shows that there are two molecules in the crystallographic asymmetric unit. The cross-polarization time constants T(CP) and relaxation times in the rotating frame T(1rho)H were obtained from the variable-contact cross-polarization experiments for tigogenin and diosgenin. The values of T(CH) for methyl carbons indicate fast rotation of methyl groups and are close (0.30-0.35 ms), suggesting that the interaction with their intramolecular neighbors is similar. The values of T(1rho)H for carbons of tigogenin are longer than of diosgenin. Very efficient cross-polarization dynamics results in short time required for obtaining a spectrum of sapogenin of remarkably good quality.     

雪胆素C的1H和13C NMR化学位移完全归属

雪胆素C是一个雪胆素甲在碱性条件下，乙酰基转移产生的同分异构体. 文中报道了应用¹³C NMR-DEPT、¹H-¹H COSY, NOESY, ¹³C-¹H COSY等多种NMR技术，对雪胆素C的NMR碳氢化学位移完全指定.     

1H and 13C NMR studies of molecular dynamics in the biocopolymer of glycolide and epsilon-caprolactone

Copolymers of glycolide and epsilon-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T, relaxation is dominated by trans-gauche isomerisation, with an activation energy of 34-35 kJ mol(-1).     

应用二维谱学技术归属泰妥拉唑的1H和13C NMR

应用DEPT（无畸变极化转移增强谱）、HMQC（异核多量子相干谱）、HMBC（异核多键相干谱）、¹H-¹H COSY（相关谱）、NOESY（核欧沃豪斯谱）和 TOCSY（全相关谱）谱学技术,对泰妥拉唑所有的氢进行了归属. 不对称硫原子引起邻接CH₂ 2个氢化学位移不等价;该2个氢相互偶合,其偶合常数为12.9 Hz;借助DEPT谱,2个甲氧基被区别;借助DEPT和TOCSY谱,另2个与碳相连的甲基被区分;利用HMBC谱,所有的碳峰可以归属.      

多取代(口山)酮及其糖甙(口山)酮的1H和13C NMR研究

总结了作者所测定过的多取代(口山)酮及其糖甙类衍生物的¹H和¹³C NMR位移数据,着重就取代基与结构的关系进行了探讨,认为多取代(口山)酮1位和8位取代情况直接影响着其他位置的化学位移数值,这一现象可以直接用于该类化合物的结构鉴定.     

In-situ NMR studies of isobutane activation and exchange in zeolite beta

¹H solid-state NMR techniques have been used to simultaneously detect the reactivity of both catalyst and alkane reactant protons in an in-situ experimental design. Specifically, the activation of isobutane C–H bonds by the solid acid zeolite H-Beta is directly observed while the reaction is in progress, and the rate of proton transfer between the solid catalyst surface and gaseous isobutane is quantitatively measured using isotopic ¹H/²H exchange methods. Arrhenius analysis of isothermal kinetic runs revealed an apparent activation barrier of 70 kJ/mole for the exchange process between isobutane and the 12-membered ring H-Beta, which exceeds our previously determined value of 57 kJ/mole for isobutane in the 10-membered ring H-ZSM-5 (JACS 2006, v. 128, p. 1848). Estimation of true activation energies using heat of adsorption data from the literature combined with the experimentally measured apparent E_a suggests that the true activation barrier differs by only 6–7 kJ/mole in the two catalysts. We discuss the possibility that subtle shape selectivity, or inverse shape selectivity, and lattice solvation differences between the two catalysts account for the enhanced solvation of the isobutane transition state in HZSM-5 compared to the larger channel H-Beta. In all experiments, the isobutane reagent was treated to eliminate any unsaturated impurities that might serve as initiators for carbenium-ion mechanisms, and the active catalyst was free of any organic contaminants that might serve as a source of unsaturated initiators.     

TRAPDOR double-resonance and high-resolution MAS NMR for structural and template studies in zeolite ZSM-5

A combination of ²⁷Al magic-angle spinning (MAS)/multiple-quantum (MQ) MAS, and ²⁷Al–{¹⁴N} TRAnsfer of Population in DOuble-Resonance (TRAPDOR) nuclear magnetic resonance (NMR) was used to study aluminium environments in zeolite ZSM-5. ²⁷Al–{¹⁴N} TRAPDOR experiments, in combination with ¹⁴N NMR were employed to show that the two tetrahedral peaks observed in the ²⁷Al MAS/3Q-MAS spectra of as-synthesized ZSM-5 are due to aluminium atoms occupying crystallographically inequivalent T-sites. A ¹³C–{²⁷Al} TRAPDOR experiment was used to study the template, tetrapropyl ammonium bromide (TPABr), in the three-dimensional pore system of ZSM-5. The inequivalency of the methyl groups of TPA was observed in the ¹³C–{²⁷Al} TRAPDOR spectra of as-synthesized ZSM-5 and the motion of the methyl end of the propyl chain appeared to be more restricted in the sinusoidal channel than in the straight channel.     

几种N-取代马来酰胺酸辅酶模型的核磁共振研究

我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了¹H、¹³C NMR的研究, 测得¹H、¹³C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.     

Multi-scale NMR characterisation of mesostructured materials using 1H-->13C through-bond polarisation transfer,fast MAS,and 1H spin diffusion

A NMR method for the characterisation of materials at different length scales, robust and simple to implement, is presented. It combines selection of 1H-13C pairs by a through-bond polarisation transfer (INEPT here) and exploration of larger distances by the introduction of 1H spin diffusion. This characterisation method is well adapted to the highest MAS rates and takes benefits of it. The effect of 1H dephasing on the efficiency of the 1H-->13C through-bond polarisation transfer is determined. This allows consecutively the quantification of signals. Mesostructured spherical silica-based particles containing CTA+ cations were studied by this multi-scale characterisation method. Contrasted spin diffusion curves were found and qualitatively explained by differences in terms of mobility and spatial distributions.     

High-resolution 1H and 13C NMR of solid 2-Aminobenzoic acid

Three crystalline modifications of 2-aminobenzoic acid (anthranilic acid) have been studied by ¹³C CP/MAS and ¹H CRAMPS NMR. The peaks are assigned and discussed in relation to (a) the neutral or zwitterionic nature of the molecules, (b) the crystal structures, known for two of the polymorphs, (c) residual (N,C) dipolar splittings, (d) hydrogen bonding and (e) dynamic exchange. The value of applying both types of spectroscopy to such studies is stressed.     

Quantitative characterization of coal structure by high-resolution CP/MAS 13C solid-state NMR spectroscopy

A method for quantitatively characterizing the carbon skeletal structure of coal by variable contact time experiment using high-resolution CP/MAS ¹³C solid-state NMR spectroscopy is proposed in this paper. The initial polarization transfer intensity from protons directly bonded with carbons, instead of dipolar-dephasing techniques which had to run on a lower frequency NMR spectrometer (100.02 MHz for proton), was used to divide the bridgehead and protonated aromatic carbons, making all the NMR data in this paper obtained on a high frequency NMR spectrometer (500.12 MHz for proton). On this basis, the fractions of different carbons in coal were further divided by the initial polarization transfer intensity from spin diffusion of protons unbonded with carbons. The structure of Naomaohu coal, a subbituminous coal from China, was measured. The change of polarization transfer with contact time was analyzed quantitatively. The fractions of aromatic, aliphatic, carboxyl and carbonyl carbons, and corrective aromaticity are 0.61, 0.39, 0.1 and 0.51, respectively. The fractions of protonated and bridgehead aromatic carbons are 0.22 and 0.09, respectively. These results agreed with literatures, and bond concentration calculated by the carbon skeletal structure distribution of coal was reasonable.