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SDBS includes 14700 1 H NMR spectra and 13000 13 C NMR spectra as well as FT-IR, Raman, ESR, and MS data. The data are stored and displayed as an image of the processed data. Annotation is achieved by a list of the chemical shifts correlated to letters which are also used to label a molecular line drawing.
If a spectrum of an unknown chemical compound is available, a reverse search can be carried out by entering the values of the chemical shift, frequency or mass of the peaks in the NMR, FT-IR or EI-MS spectrum respectively. This type of search affords all the chemical compounds in the database that have the entered spectral characteristics. [6]
As with NMR spectroscopy in general, good resolution requires a high signal-to-noise ratio, clear separation between peaks for each stereoisomer, and narrow line width for each peak. Chiral lanthanide shift reagents cause a clear separation of chemical shift, but they must be used in low concentrations to avoid line broadening .
The 19 F NMR chemical shifts span a range of about 800 ppm. For organofluorine compounds the range is narrower, being about −50 to −70 ppm (for CF 3 groups) to −200 to −220 ppm (for CH 2 F groups). The very wide spectral range can cause problems in recording spectra, such as poor data resolution and inaccurate integration.
This occurs most frequently in compounds that contain phosphorus or fluorine, as they are both spin-1/2 nuclei of 100% abundance. For example, the 1H signals for the protons in fluoromethane are split into a doublet by the fluorine atom; conversely, the fluorine-19 NMR spectrum of this compound shows a quartet due to being split by the three ...
For example, AB indicates two nuclei which have similar chemical shifts (Δδ similar to or smaller than J), whereas AX indicates two which lie further apart on the spectrum (Δδ significantly larger than J). A 2 B would similarly indicate a spin system containing two equivalent nuclei (A) and a third, inequivalent one (B).
Phosphorus is commonly found in organic compounds and coordination complexes (as phosphines), making it useful to measure 31 - NMR spectra routinely. Solution 31 P-NMR is one of the more routine NMR techniques because 31 P has an isotopic abundance of 100% and a relatively high gyromagnetic ratio. The 31 P nucleus also has a spin of 1 / 2 ...
NMR-active nuclei, particularly those with a spin quantum number of 1/2, are of great significance in NMR spectroscopy. Examples include 1 H, 13 C, 15 N, and 31 P. [10] Some atoms with very high spin (as 9/2 for 99 Tc atom) are also extensively studied with NMR spectroscopy. [11]