共查询到20条相似文献,搜索用时 9 毫秒
1.
2.
Israel Agranat Eliezer Aharon-Shalom Albert J. Fry Richard L. Krieger William O. Krug 《Tetrahedron》1979,35(6):733-740
The 13C NMR spectra of diferocenylcyclopropenone (1) and the triferrocenylcyclopropenium (2) and ferrocenyldiphenylcyclopropenium (3) cations in non-acidic media are analyzed with special reference to the information they afford concerning charge distribution in these species. A delocalization of the positive charge into the remote unsubstituted five-membered rings of 2 and 3 is indicated. The role of the metal as a conduit for this effect is suggested. 相似文献
3.
Molecular self-diffusion coefficients (D) of species in solution are related to size and shape and can be used for studying association phenomena. Pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy has been revealed to be a powerful analytical tool for D measurement in different research fields. The present work briefly illustrates the use of PFG-NMR for assessing the existence of interactions in very different chemical systems: organic and organometallic compounds, colloidal materials and biological aggregates. The application of PFG-NMR is remarkable for understanding the role of anions in homogenous transition metal catalysis and for assessing the aggregation behaviour of biopolymers in material science. 相似文献
4.
The PMR spectra of the condensation products of N-arylsulfonylmonoimino sulfur dioxide with the dienes were studied. It was established that the reaction goes according to the condensation pattern of the Diels-Alder reaction, involving the nitrogen sulfur double bond with the formation of 1-oxo-2-arylsulfonyl-3, 6-dihydro-1, 2-thiazines. 相似文献
5.
The PMR spectra of the condensation products of N-arylsulfonylmonoimino sulfur dioxide with the dienes were studied. It was established that the reaction goes according to the condensation pattern of the Diels-Alder reaction, involving the nitrogen sulfur double bond with the formation of 1-oxo-2-arylsulfonyl-3, 6-dihydro-1, 2-thiazines.For part V, see [13]. 相似文献
6.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1990,46(6):1027-1033
The 1H and 13C NMR spectra of three isomeric dinaphthothiophenes are recorded. Chemical shift assignments were made on the basis of substituent chemical shift (SCS) effect arguments, coupling considerations, proton—proton auto-correlated homonulcear (COSY) two-dimensional spectroscopy, and proton—carbon heteronuclear correlation (HETCOR) two-dimensional spectroscopy. Some previously published 1H chemical shifts and coupling constants are compared with our data and some divergences are noted. 相似文献
7.
Nuclear magnetic resonance (NMR), as a powerful technology, is widely used to characterize the physicochemical properties of surfactants in solution. As a sensitive technique to molecular environment, NMR is beyond the reach of other spectral methods in surfactant systems. Recent years, intensive investigations of surfactants by NMR were reported but not well summarized; therefore, we highlight these significant progresses, which may shed light on the challenges to understand their behavior and mechanisms in surfactant systems. The theory of various NMR methods was introduced, including chemical shifts, diffusion, relaxation, 2D nuclear Overhauser effect spectroscopy and rotating frame nuclear Overhauser effect spectroscopy. The behavior, interaction, and mechanisms among surfactants and other molecules from NMR technologies were discussed. Challenges to understand the behavior and mechanisms in surfactant systems and instrumentation limits are addressed as perspectives. 相似文献
8.
A method to calculate NMR J-coupling constants from first principles in extended systems is presented. It is based on density functional theory and is formulated within a planewave-pseudopotential framework. The all-electron properties are recovered using the projector augmented wave approach. The method is validated by comparison with existing quantum chemical calculations of solution-state systems and with experimental data. The approach has also been applied to the silicophosphate, Si(5)O(PO(4))(6), giving (31)P-(29)Si-couplings which are in excellent agreement with experiment. 相似文献
9.
Leah B. Casabianca 《Magnetic resonance in chemistry : MRC》2020,58(7):611-624
The nuclear magnetic resonance (NMR) chemical shift is extremely sensitive to molecular geometry, hydrogen bonding, solvent, temperature, pH, and concentration. Calculated magnetic shielding constants, converted to chemical shifts, can be valuable aids in NMR peak assignment and can also give detailed information about molecular geometry and intermolecular effects. Calculating chemical shifts in solution is complicated by the need to include solvent effects and conformational averaging. Here, we review the current state of NMR chemical shift calculations in solution, beginning with an introduction to the theory of calculating magnetic shielding in general, then covering methods for inclusion of solvent effects and conformational averaging, and finally discussing examples of applications using calculated chemical shifts to gain detailed structural information. 相似文献
10.
Quantitative determination of aluminium in tea by means of aluminium-27 nuclear magnetic resonance spectroscopy 总被引:2,自引:0,他引:2
K R Koch 《The Analyst》1990,115(6):823-825
A method for determining the Al levels in tea leaf digests and tea infusions by means of 27Al nuclear magnetic resonance (NMR) spectroscopy is described. Quantitative results down to 2.0 micrograms cm-3 of Al in 0.5-cm-3 acidified samples are readily obtainable in standard 5-mm NMR tubes. An acceptable quantitative determination is achieved by using an internal Al standard in a 1-mm capillary in conjunction with europium nitrate as a shift reagent. 相似文献
11.
R. A. Assink 《Journal of Polymer Science.Polymer Physics》1977,15(1):59-69
Polyurethanes are block copolymers composed of hard and soft segments which often undergo microphase separation with the resultant formation of hard and soft domains. The nuclear-magnetic-free induction decay of such systems is shown to consist of a fast Gaussian component corresponding to glassy domains and a slow exponential component corresponding to rubbery domains. Thus, by being sensitive to the microscopic mobility of a material, nuclear magnetic resonance (NMR) has the potential to determine when a polyurethane has separated into domains and the relative amounts of material in each domain. After annealing the free-induction decay of a linear polyurethane showed a distribution of relaxation times indicating that mixing of the domains had taken place and a continuum of compositions exist in the material. The free-induction decay of a cross-linked polyurethane was unaffected by annealing, confirming the results of an earlier study. 相似文献
12.
In the PMR spectrum of 8-phenylpurines, the multiplet of the o-protons appears downfield of the multiplet, characteristic for m,p-protons. The separation of the centres of these two signals (Δ-value) diminishes with increasing steric interference between the phenyl ring and substituents in the imidazole moiety. The contribution of the purine ring current to the chemical shifts of the aromatic protons was calculated according to the theory of Johnson and Bovey, and the torsion angles θ between the phenyl ring and the plane of the purine system were derived. For 8-phenylpurines with an NH-group in the imidazole ring, θ is 10–15°; for compounds with an N-methyl group in this ring, θ ≈ 35–45°; in 3,9-dimethyl derivatives, Δ becomes zero, while θ is about 50°. 相似文献
13.
J. Clements J. Humphreys I. M. Ward 《Journal of Polymer Science.Polymer Physics》1986,24(10):2293-2305
Broad-line nuclear magnetic resonance (NMR) measurements have been carried out for the proton resonance in an oriented liquid-crystalline copolyster prepared from 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA). The Second moments were determined as a function of the angle γ between the specimen orientation direction and the static magnetic field. The low-temperature NMR results are consistent with a rigid structure of random copolymer chains arranged on a hexagonal lattice. As the temperature is raised the NMR signal changes and can be modeled very satisfactorily by considering that there is free rotation of the benzene ring residues about the 1-4 substitution direction. At more elevated temperatures the observed NMR spectra are consistent with rotation of both HBA and HNA groups. 相似文献
14.
The system phenol-CCl4 was studied by measuring proton and deuteron magnetic relaxation rates and self-diffusion coefficients at 25°C. From these data intermolecular relaxation rates have been calculated. By means of an association parameter A, association of phenol molecules with respect to various parts of the molecule has been established. Closest distances of approach between protons and configurations of maximum occurrence probabilities are reported. 相似文献
15.
16.
V. P. Yurkinskii E. G. Firsova O. V. Chechulina A. M. Soboleva 《Russian Journal of Applied Chemistry》2008,81(9):1549-1553
Electrical conductivity of lithium chloride solutions in the system isopropyl alcohol-water in the temperature range 290–323 K was studied. The dependences of the specific and molar electrical conductivity of the solutions on the concentration of water and lithium chloride were determined. 相似文献
17.
18.
Douglas R. Chrisope Rebecca A. Keel Alfons L. Baumstark David W. Boykin 《Journal of heterocyclic chemistry》1981,18(4):795-798
The carbon-13 nmr spectra of a series of 3-aryl-5-phenylisoxazoles (I) and 3-phenyl-5-arylisoxazoles (II) have been recorded and the signals assigned. Carbon-13 data for series I show little effect of substituent on the chemical shift of the isoxazole ring carbons. However, a plot of the carbon-13 chemical shift of carbon-5 in the isoxazole system I versus the chemical shift of carbon-3 in the 3-(4′-aryl)-1-phenylpropenones gives a straight line (r = .989) with a slope of 0.35. In series II, the chemical shifts of both carbon-4 and -5 are relatively sensitive to substituent effects. Fair correlations between Hammett sigma values and the chemical shifts of these two carbons are found; dual substituent parameter treatment improves the correlations. The results obtained from correlations with carbon-4 in series II are similar to those obtained from β-carbons of a number of styrene systems. The data show that carbon-4 in series II is approximately 20% less sensitive to substituent effects than the previously reported data for carbon-3 of 2-arylfurans. Transmission of substituent effects in the isoxazole system compare well with those of the benzothiazole system. 相似文献
19.
Enzyme--substrate interaction by nuclear magnetic resonance 总被引:2,自引:0,他引:2