Nuclear magnetic resonance spectral parameters

Over the past 40 years fluorine nuclear magnetic resonance (19F-NMR) spectroscopy has become the most prominent instrumental method for structure elucidation of organofluorine compounds. Consequently the amount of spectral data published has grown almost exponentially Unfortunately NMR data for fluonnated compounds are not as well, or as easily, organized as proton data To facilitate retrieval of fluorine NMR information and comparison of data, acquisition parameters should be clearly defined Guidelines for publication of NMR data have been established by the International Union for Pure and Applied Chemistry (IUPAC) [7] The following niles for acquisition and reporting of NMR data should be strictly observed... 

Besides the direct relations between orbitals and spectroscopy outlined above, there are many indirect relations which have to do with the interpretation of various spectral parameters in other branches of spectroscopy. We shall illustrate this with the main spectral parameters in nuclear magnetic resonance spectroscopy NMR chemical shifts and nuclear spin-spin coupling constants. 

NMR. Quantitative liquid-state carbon-13 nuclear magnetic resonance ( 3c NMR) spectra were recorded for humic and fulvic acid from Como Creek foam and for stream and foam fulvic- and humic- acid samples from the Suwannee River at the U.S. Geological Survey, laboratory in Arvada, CO. C NMR could not be performed on other humic substances due to insufficient sample or instrument availability. The acquisition parameters used were as follows C NMR spectra were recorded on a Varian XL-300 NMR spectrometer at 75 MHz. Each sample (200 mg of freeze-dried material) was dissolved in deuterated water and deuterated sodium hydroxide was added to ensure solution a total solution volume of approximately 6 to 7 mL. Spectra were recorded using a 30,000 Hz spectral window, a 45 pulse width, a 0.199 second acquisition time, and a pulse delay of 10 seconds for quantitative spectra. The number of transients was 10,000, and line broadening was 50 Hz. 

There are a variety of techniques for the determination of the various parameters of the spin-Hamiltonian. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR), Electron Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occassionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detection of Magnetic Resonance (ODMR), Atomic Beam Spectroscopy and Optical Spectroscopy. The extraction of the magnetic parameters from the spectra obtained by application of these and related techniques follows procedures which may in detail depend on the technique, the state of the sample (gaseous, liquid, unordered solid, ordered solid) and on spectral resolution. For particulars, the reader is referred to the general references (D). 

Solid-state nuclear magnetic resonance (NMR) is nowadays an established technique in the pharmaceutical industry, used mainly as a tool to distinguish different polymorphs. Its advantages are high versatility and resolution, which allow for studies of aU the materials in a formulation. Compared to, for example, powder XRPD and Raman scattering, spectral overlap is most often much less of a problem in NMR. Also, the primary parameter, the resonance frequency or the chemical shift, is very sensitive not only to the intramolecular structure but also to intermolecular interactions and spatial arrangement, which is the basis for polymorph selectivity. A range of nuclei can be studied for complementary information, for example, H, N, and T. 

Around 1950, it was discovered that nuclear resonance frequencies depend not only on the nature of the atomic nuclei, but also on their chemical environment. The possibility of using NMR as a tool for chemical analysis soon became apparent. All applications of solution NMR spectroscopy make use of one or more of the spectral parameters chemical shift, spin-spin coupling, signal intensity, and relaxation time. In the following sections examples from h and C NMR are used but the concepts described apply to magnetic nuclei in general. 

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