Chemical shift ranges, nuclear magnetic

The ultimate molecular level characterization of a pharmaceutical material is performed on the level of individual chemical environments of each atom in the compound, and this information is best obtained using nuclear magnetic resonance (NMR) spectroscopy. Advances in instrumentation and computer pulse sequences currently allow these studies to be carried out routinely in the solid state.2 Although any nucleus that can be studied in the solution phase also can be studied in the solid state, most work has focused on studies. H-NMR remains an extremely difficult measurement in the solid state, and the data obtained from such work can be obtained only at medium resolution. The main problem is that H-NMR has one of the smallest isotropic chemical shift ranges (12 ppm), but has peak broadening effects that can span several parts per million in magnitude. 

The natural stable isotope of fluorine, fluorine-19 (19F), with a spin of one-half and a chemical shift range of around 300 ppm, is a sensitive and useful probe in nuclear magnetic resonance (NMR) studies. Fluorine substitution may be a very effective method for studying the fate of bioactive molecules. Since there are few natural fluorinated materials to create background signals, the analyses are freed from the complications often associated with proton NMR spectroscopy (65). An artificially prepared useful short-lived isotope, fluorine-18 (18F), decays by positron emission. Positron emission tomography (PET) is an especially useful non-invasive... 

Figure 2 (A) chemical shift ranges of selected selenium functionalities (excluding metal complexes). (B) Se chemical shift ranges of compounds containing C=Se groups (excluding metal complexes). Reproduced by permission of John Wiley and Sons from Duddeck H (1996) Sulfur, selenium and tellurium NMR. In Grant DM and Harris RK (eds) Encyclopedia of Nuclear Magnetic Resonance, pp 4623-4635. Copyright 1996. John Wiley Sons.

Nuclear Magnetic Resonance Spectroscopy. Nmr is a most valuable technique for stmeture determination in thiophene chemistry, especially because spectral interpretation is much easier in the thiophene series compared to benzene derivatives. Chemical shifts in proton nmr are well documented for thiophene (CDCl ), 6 = 7.12, 7.34, 7.34, and 7.12 ppm. Coupling constants occur in well-defined ranges J2-3 = 4.9-5.8 ... 

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