Couplings, homonuclear

Homonuclear teclmiques such as J-resolved spectroscopy also exist for rotatmg all multiplets tlirough 90°, to resolve overlaps and also give a ID spectrum from which all homonuclear couplings have been removed [26]. 

In a coupled spin system, the number of observed lines in a spectrum does not match the number of independent z magnetizations and, fiirthennore, the spectra depend on the flip angle of the pulse used to observe them. Because of the complicated spectroscopy of homonuclear coupled spins, it is only recently that selective inversions in simple coupled spin systems [23] have been studied. This means that slow chemical exchange can be studied using proton spectra without the requirement of single characteristic peaks, such as methyl groups. 

Observation of homonuclear coupling is very unlikely because of the low probabiHty for bonding between two atoms. In addition,... 

Titman, J. J., Keeler, J. Measurement of homonuclear coupling constants from NMR correlation spectra. J. Magn. Reson. 1990, 89, 640-646. 

Figure 18 Hypothetical CnHn—C2H2—C3H3 fragment within a more complex molecule, with heteronuclear coupling constants Vhici, 2Jmc2> Vh2ct> 21h2ci> respectively, and homonuclear coupling constants Vhih2, Vmm, respectively.

Prior to the advent of homonuclear 2D-NMR experiments, it was necessary to rigorously interpret a proton NMR experiment and identify all of the homonuclear couplings to assemble the structure. Alternatively, there are multi-dimensional NMR experiments that provide similar information in a more readily interpretable way. 

As in many other aspects of polymer stereochemistry, polypropylene also plays a central role in NMR spectroscopy. Since 1962 numerous articles have dealt with the interpretation of its proton spectrum (125-128) the state of knowledge at the end of that decade has been well described by Woodbrey (117). The difficulty in this study stems fiom two factors The narrow frequency range comprising the entire spectmm and the large homonuclear coupling between CH2, CH, and CH3 protons. The whole spectrum is within a range of <1.5... 

In this chapter, the discussion will be focused on the ID TOCSY (TO-tal Correlation SpectroscopY) [2] experiment, which, together with ID NOESY, is probably the most frequently and routinely used selective ID experiment for elucidating the spin-spin coupling network, and obtaining homonuclear coupling constants. We will first review the development of this technique and the essential features of the pulse sequence. In the second section, we will discuss the practical aspects of this experiment, including the choice of the selective (shaped) pulse, the phase difference of the hard and soft pulses, and the use of the z-filter. The application of the ID TOCSY pulse sequence will be illustrated by examples in oligosaccharides, peptides and mixtures in Section 3. Finally, modifications and extensions of the basic ID TOCSY experiment and their applications will be reviewed briefly in Section 4. 

Homonuclear coupling constants can also be determined from these subspectra with good digital resolution and relative free of overlap of signals. 

Performing the CPMG experiment on a spin system with homonuclear coupling introduces the complication of echo modulation by the scalar couplings [4, 5, 7, 36]. This makes transverse proton relaxation measurements... 

Homonuclear coupling, 143 Horseradish, 337 Hydrogen lamp, 199 Hydrostatic injection, 117 Hyphenated technique, 8 Hypsochromic effect, 195... 

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