Nuclear magnetic resonance Temperature-dependent

Meyer, C., Pascui, O., Reichert, D., Sander, L.C., Wise, S.A., and Albert, K., Conformational temperature dependence of a poly(ethylene-co-acrylic acid) stationary-phase investigated by nuclear magnetic resonance spectroscopy and liquid chromatography, J. Sep. Set, 29, 820, 2006. 

Changes In nuclear magnetic resonance measurements of an extensive suite of Australian coals on heating and exposure to pyridine are used to elucidate the molecular conformation of coal macerals Two types of fusible material are Identified In these coals One Is associated with llptlnltes of all ranks and Is typified by fusion commencing at temperatures below 475 K. The other Is associated with vltrlnltes and some Inertlnltes of bituminous coals only and Is characterized by a sharp onset of fusion at temperatures above 625 K. The temperature of onset of fusion Increases with rank for both types The effect of pyridine on the molecular stability of bituminous coals at ambient conditions Is strongly dependent on maceral composition at 86% C and on rank at higher carbon contents ... 

One of the most powerful tools in the study of carbocations is nuclear magnetic resonance (NMR) spectroscopy. This method yields direct information—through chemical shifts, coupling constants, and the temperature dependence of band shapes— about the structure and dynamics of carbocations. 

Self diffusion coefficients can be obtained from the rate of diffusion of isotopically labeled solvent molecules as well as from nuclear magnetic resonance band widths. The self-diffusion coefficient of water at 25°C is D= 2.27 x 10-5 cm2 s 1, and that of heavy water, D20, is 1.87 x 10-5 cm2 s 1. Values for many solvents at 25 °C, in 10-5 cm2 s 1, are shown in Table 3.9. The diffusion coefficient for all solvents depends strongly on the temperature, similarly to the viscosity, following an Arrhenius-type expression D=Ad exp( AEq/RT). In fact, for solvents that can be described as being globular (see above), the Stokes-Einstein expression holds ... 

In this experiment, nuclear magnetic resonance (NMR) techniques will be used to determine the specific rate constants and for the forward and reverse reactions as well as the value for the equilibrium constant K. Like the hydrolysis of many other organic compounds, this reaction can be acid catalyzed and the effect of hydrogen-ion concentration on the kinetics can be studied. Furthermore, the dependence of y, , and K on temperature will be measured and used to evaluate activation energies. 

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