Nuclear magnetic resonance dynamics

It has been demonstrated that the model works well with a wide range of heterogeneous environments including pores, channels, surfaces, and gels and a collection of hosting materials such as silica, alumina, titania, and clays [63-66]. As the exact molar fraction and relaxation time for the surface-adsorbed molecules are difficult to determine, the experimental results are often used as a relative comparison among samples with similar compositions. For example, relative surface area or particle size can be estimated for two slurry samples with a similar Tij value based on their observed relaxation times [67]. 

As the relaxation time for the surface-adsorbed molecules is mainly determined by the molecular interaction between the adsorbed molecules and the surface of interest, a comparison among samples with different surface properties may yield information on these at a molecular level. For example, when two silica slurry samples are investigated, a sample with a rich content of hydroxyl group should possess a smaller T ox T2 corrected with particle size and surface area differences. 

FIGURE 2.22 Correlation among hydroxyl content on surface, material removal rates for 71, and Ti relaxation slopes measured using DMNR technique. 

Pulsed field gradient NMR (PFG-NMR) is a powerful, nondestructive technique of measuring self-diffusion coefficients in a colloidal dispersion [69-71]. Molecules associated with an aggregate or a particle will diffuse more slowly than their free dissolving state. More specifically, when a water-soluble species is partially adsorbed onto an abrasive particle, the measured overall diffusion coefficient (D ) of the species is decreased. If the diffusion coefficient of the free dissolving species can be measured in the absence 

FIGURE 2.23 Dependence of partition coefficient on the concentration of BTA in an aqueous environment, where 1 = 100% free dissolving in water and 0 = 100% encapsulated. Sample 1 contains 1 mM of BTA and no surfactant. Sample 2 contains 1 mM of BTA and 5 mM (below cmc) of sodium dodecyl sulfate (SDS). Sample 3 contains 1 mM of BTA and 15mM of SDS. Sample 4 contains 1 mM of BTA and 30 mM of SDS. Addition of 100 ppm of copper (II) nitrate to sample 4 results in sample 5. Addition of 300 ppm of copper ions to sample 5 results in sample 6 (from Ref. [72]). 

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Freeman R and Hiii H D W 1975 Determination of spin-spin reiaxation time in high-resoiution NMR Dynamic Nuclear Magnetic Resonance Spectroscopy e6 L M Jaokman and F A Cotton (New York Aoademio) p 131-62... 

Jaokman L M and Cotton F A 1975 Dynamic Nuclear Magnetic Resonance Spectroscopy (New York Aoademio)... 

Gutowsky H S and Holm C H 1975 Time-dependent magnetic perturbations Dynamic Nuclear Magnetic Resonance Spectroscopy ed L M Jackman and F A Cotton (New York Academic) pp 1-21... 

The barriers to rotation about the N-C bond have been determined b dynamic nuclear magnetic resonance for A -isopropyl (80. 81). propanoic acid (74). A -ethyl (82). N-benzyl. and A -neopentyl substituents (82). Selected values of these barriers are given in Tables VII-6 and VII-7. 

TABLE VIL6. BARRIERS TO ROTATION AROUND sp- -sp BOND FOR VARIOUS 3-SUBSTITUENTS IN THE A-4-THIAZ0LINE-2-TH10NE SERIES OBTAINED BY DYNAMIC NUCLEAR MAGNETIC RESONANCE. 

BalK82 Balasubramanian, K. Topological and group theoretical analysis of dynamics nuclear magnetic resonance spectroscopy. J. Phys. Chem. 86 (1982) 4668-4674. 

Binsch, G., The Study of Intramolecular Rate Processes by Dynamic Nuclear Magnetic Resonance, 3, 97. 

Simulation of Dynamic Nuclear Magnetic Resonance Spectra for Systems with Many Spins or Exchange Sites. 

Binsch, G. Band-Shape Analysis." In Dynamic Nuclear Magnetic Resonance Spectroscopy Jackman, L. M. Cotton, F. A., Eds. Academic Press New York, 1975 pp. 45-81. See also Binsch, G. Top Stereochem., 1968, 3, 97-192. 

G. Binsch in Dynamic Nuclear Magnetic Resonance Spectroscopy, L. M. Jackman and F. A. Cotton, eds. Academic Press, NY, 1975, Chap. 3. 

B-75M15I900 F. A. L. Anet and R. Anet in Dynamic Nuclear Magnetic Resonance Spectro-... 

Exchange Rate Measurements Based on Line-Shape Analysis (DNMR Dynamic Nuclear Magnetic Resonance). Under the measurable exchange rate conditions, two possibilities have been considered ... 

The term DNMR, Dynamic Nuclear Magnetic Resonance, refers to the process of recording and usually computer simulating exchange broadened NMR spectra at a number of temperatures in order to determine mechanistic and/or kinetic information. b The terms fast and slow are used rather than the more familiar labile and nonlabile because the latter imply an intermolecular reaction. 

After a short qualitative introduction to the principles of dynamic nuclear magnetic resonance spectroscopy , the proposed interconversion processes for cycloheptanes and cycloheptenes are explained in detail. According to calculations, the most favourable conformation for cycloheptanes seems to be the twist chair cycloheptenes prefer the chair form. Possible conformational processes for chair and boat forms are discussed and illustrated. 

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