Nuclear magnetic resonance reference compound

The nuclear magnetic resonance (NMR) spectra (300MFIz) of both the compound 10 and 11 was recorded in dimethyl sulfoxide (DMSO-r4) and CDCI3. The compound 10 in its H NMR spectrum showed a singlet signal at 5 5.32 due to the two NH protons, whereas compound 11 showed the presence of two NH protons at 6 6.80 <1989JOC3062>. For information on spectral studies of the compounds 1-5, refer to CHEC-II(1996) <1996CHEC-II(8)707>. 

Almost all the reported compounds have been characterized with the help of various nuclear magnetic resonance (NMR) techniques. For previous studies of the compounds, refer to CHEC-II(1996) <1996CHEC-II(8)713>.The H NMR spectrum (300MHz) of 2,3,7-trirnethyl-3a,9a-dihydro-1,8-dithiaMa,5,9-triazacyclopenta[3]naphthalene-4,6-dione 47 <2000JHC1161> showed the presence of one quartet at 8 4.23 corresponding to the CH. Another broad singlet corresponds to the presence of the N-H proton. 

Concentrations can be measured with a spectrophotometer10 or by nuclear magnetic resonance,11 so pKa for CH+ can be determined. Then, with CH as the reference, the pKz for another compound, DH r, can be measured. This procedure can be extended to measure the strengths of successively weaker bases (such as nitrobenzene, p/fa =—11.38), far too weak to be protonated in water. 

Tor reference. Positive identification can be made only by collecting the compound or transierring it as it elutes directly into another apparatus for analysis by other means, such as infrared or ultraviolet spectroscopy, mass spectrometry, or nuclear magnetic resonance. Commercially available apparatus is available which combines in a single unit both a gas chromatograph and an infrared, ultraviolet, or mass spectrometer for routine separation and identilicalion. The ancillary system may also be microprocessor-based, with an extensive memory for storing libraries of known infrared spectra or fragmentation patterns (in the case of mass spectrometers). Such systems allow microprocessor-controlled comparison and identilicalion of detected compounds. 

Incorporation studies of C-labeled precursors require extensive nuclear magnetic resonance (NMR) measurements. The signals of C-NMR-spectra of the analyzed metabolites must be assigned fully. The C-NMR spectra of the reference compound of natural abundance (1.1%) and of the labeled metabolite must be recorded in the same conditions. A comparison between the relative signal intensities of the two spectra indicates that the carbon atom is labeled and indicates the magnitude of the isotope enrichment. 

Obtain infrared and nuclear magnetic resonance spectra following the procedures of Chapters 19 and 20. If these spectra indicate the presence of conjugated double bonds, aromatic rings, or conjugated carbonyl compounds obtain the ultraviolet spectrum following the procedures of Chapter 21. Interpret the spectra as fully as possible by reference to the sources cited at the end of the various spectroscopy chapters. 

Table 4 Magnesium-25 Nuclear Magnetic Resonance Data for Organic Solutions of Magnesium Compounds Relative to MgS04-7H20 (0.18 mol/L) as External Reference...

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