Proton magnetic resonance spectroscopy continued

Godejohann M, M Astratov, A Preiss, K Levsen, C Miigge (1998) Application of continuous-flow HPLC-proton-nuclear magnetic resonance spectroscopy and HPLC-thermospray spectroscopy for the structrual elucidation of phototransformation products of 2,4,6-trinitrotoluene. Anal Chem 70 4104-4110. 

Nuclear magnetic resonance spectroscopy plays a major part in the elucidation of the structures of these bases, and continues to be the most valuable technique in structural work in the series. Pulsed nmr difference spectroscopy of small nuclear Overhauser effects between aromatic protons and o-methyl and /-methyl groups has permitted differentiation between two possible isomeric structures for dihydrodaphnine (D. Neuhaus et al.. Tetrahedron Letters, 1981, 2933. 

Supercritical fluid chromatography was coupled online to Proton High Field Nuclear Magnetic Resonance Spectroscopy by an specially designed pressure-proof continuous-flow probe head. Separation of phthalate esters was carried out under supercritical conditions using carbon dioxide as eluent. ... 

TTie TOCSY 2D NMR experiment correlates all protons of a spin system, not just those directly connected via three chemical bonds. For the protein example, the alpha proton, Ft , and all the other protons are able to transfer magnetization to the beta, gamma, delta, and epsilon protons if they are connected by a continuous chain—that is, the continuous chain of protons in the side chains of the individual amino acids making up the protein. The COSY and TOCSY experiments are used to build so-called spin systems—that is, a list of resonances of the chemical shift of the peptide main chain proton, the alpha proton(s), and all other protons from each aa side chain. Which chemical shifts correspond to which nuclei in the spin system is determined by the conventional correlation spectroscopy connectivities and the fact that different types of protons have characteristic chemical shifts. To connect the different spin systems in a sequential order, the nuclear Overhauser effect spectroscopy... 

A major consequence of the introduction of pulse (FT) NMR spectroscopy has been ready access to C data - limited prior to 1970 by factors which render this magnetic nucleus relatively insensitive to continuous wave methods of recording NMR spectra (1 % natural abundance, and low value of the nuclear magnetic moment compared with that of a proton). C-NMR spectra are generally much simpler than corresponding H spectra. When run under conditions where all couplings to protons are removed (by simultaneous wide-band irradiation of proton resonances), a C-NMR spectrum consists of a series of sharp lines, each of which corresponds to the resonance of a nucleus (or nuclei) of specific magnetic environment. Further, since the chemical shift spread of C nuclei (0-200 ppm) is about 20-times that of protons. 

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