Two-Dimensional 2D NMR Techniques

Chapter 9 Nudear Magnetic Resonance and Mass Spectrometry 

Therefore, it is readily apparent which hydrogens are attached to which carbons. 

NMR signal at 67 ppm arises from the alcohol carbon (C2). Finally, from the H NMR peaks at 3.4-3.5 ppm for the two hydrogens on the carbon bearing the chlorine, our interpretation leads us out to the cross peak and down to the peak at 51 ppm (Cl). 

by a combination of COSY and HETCOR spectra, all and peaks can be unambiguously assigned to their respective carbon and hydrogen atoms in l-chloro-2-propanol. (In this simple example using l-chloro-2-propanol, we could have arrived at complete assignment of these spectra without COSY and HETCOR data. For many compounds, however, the assignments are quite difficult to make without the aid of these 2D NMR techniques.) 

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The use of two-dimensional (2D) NMR techniques has become almost routine for detailed analysis of complex organic molecules containing carbon and hydrogen. In contrast, 2D 19F NMR methods are not nearly so commonly used in the analysis of fluorine-containing molecules. The reasons for this are generally a combination of instrumental requirements combined with intrinsic differences between fluorine and proton NMR, in particular the wide range of 19F chemical shifts, which to an extent negates the need for 2D, but also can create problems, for example with respect to uniform excitation of the entire 19F band width. 

Most of the betalain pigments described in the 1960s have not been characterized by mass or NMR spectra. With FAB MS now at hand, the molecular ions of underivatized betalains can be easily determined, and the sensitivity of high-field NMR spectrometers allows the complete structural assignment, even of small samples. For the structural determination of oligosaccharide moieties, modem two-dimensional (2D) NMR techniques are now the method of choice. 

In what, it is hoped, will be the final word on the NMR chemical shift assignments of 9-methoxyellipticine (2), Commenges and Rao (52) have revised several of the C-NMR assignments published earlier by Sainsbury and coworkers (55). In the present work, a combination of two-dimensional (2D) NMR techniques ( H- H homonuclear and heteronuclear chemical shift cor-... 

Indirect detection of " Sn NMR signals, in general by NMR, using various types of two-dimensional (2D) NMR techniques (HMQC, HMBC, HSQC) enables one to study fairly dilute solutions... 

Two-Dimensional (2D) NMR Techniques 428 THE CHEMISTRY OF... Magnetic Resonance Imaging in Medicine 431... 

Among the many applications of NMR techniques, the most essential application of NMR is the characterization of molecular structures of polymeric proton-conducting materials, in terms of one-dimensional (ID) and two-dimensional (2D) NMR techniques. The second type of application is to characterize the dynamic properties of protons, water, and alcohol molecules. These dynamic properties are directly related to the mobility of protons, the macroscopic transport of water in terms of difilision and the electroosmosis, and the alcohol crossover or permeability, respectively. The third type of application is related to the identification of the water types soaked in the proton exchange membranes and the visuafization of water distribution in the proton exchange membranes. 

Following on from the one-dimensional proton and carbon spectra, the next step is to employ more sophisticated two-dimensional (2D) NMR techniques to help determine linkages within the molecule. In most of these experiments the instrument automatically combines the results of these experiments and the data... 

Recently developed two-dimensional (2D) NMR techniques can be used to determine the coupling between nuclei and to reveal the chemical shifts of these nuclei [23,24]. These new techniques largely replace a wide variety of selective spin-decoupling experiments. 

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