Nuclear magnetic resonance chemical displacement

The majority of trichloroethylene present on soil surfaces will volatilize to the atmosphere or leach into the subsurface. Once trichloroethylene leaches into the soil, it appears not to become chemically transformed or undergo covalent bonding with soil components. When trichloroethylene was absorbed onto kaolinite and bentonite, the nuclear magnetic resonance (NMR) spectra showed no evidence of chemical reactions (Jurkiewicz and Maciel 1995). Because trichloroethylene is a dense nonaqueous phase liquid, it can move through the imsaturated zone into the saturated zone where it can displace soil pore water (Wershaw et al. 1994). 

Nuclear magnetic resonance (NMR) spectroscopy is routinely applied to small carbohydrate molecules. NMR spectroscopy is based on the principle that radiofrequencies are absorbed by hydrogen and carbon atoms ( H and 13C) spinning in one of two directions (spin quantum number +1 /2) in a magnetic field. In liquids, absorption is recorded as sharp peaks. The frequency displacement (chemical shift) is a function of the H and 1SC surroundings. +A is proportional to the number of photons absorbed between these two quantum states, correlating well with anomeric and... 

An important contribution to the problem of ir-electron bonding with seven-membered rings is probably made by measurements of the chemical shifts of ring protons as studied by the nuclear magnetic resonance method. It has recently been shown (117) that the displacement of the electron density of the ring protons increases along the series (CsHs)", CeHe, ( 7117)+. Perhaps this expresses the decreasing tendency to enter stable ir-bonds. 

Nuclear magnetic resonance spectroscopy first aroused the chemist s Interest when the discovery was made that the exact nuclear precession frequency is dependent upon the chemical environment of the nucleus. The displacement of the resonance frequency relative to an arbitrary standard is commonly referred to as chemical shift. Without this property, NMR would be without practical utility to the chemist as an analytical tool and it would probably long be extinct. 

In contrast with chemical diffusion, the self- (or intra-or tracer-) diffusion of ions simply is the manifestation of Brownian motion. It can be visualized by labeling a small amount of ions and observing their displacement in an environment of nonlabeled ions of the same type. Nuclear magnetic resonance (NMR) spin-echo experiments use spin labeling radioactive tracers are used in closed capillary methods. At infinite dilution the self-diffusion of an ion X, is linked to its limiting ion conductivity Eq. (43), and its generalized mobility a>,, Eq. (15), (F = CoNa, Earaday constant) ... 

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