Homonuclear 2D NMR

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. 

It still looks pretty messy, but there are only four terms the V and / components of Ha in-phase magnetization (first and third terms), and the V and / components of Ha magnetization that is antiphase with respect to the spin state (a or f)) of the coupled Hb spin (second and fourth terms). This is a full description of what happens to the Ha magnetization that started on the -/ axis at the beginning of the l period, and it can be applied to all homonuclear 2D NMR experiments. 

Figure 1.8. Scheme for homonuclear 2D NMR. The dotted lines indicate the bounds of the mixing period (or mixing pulse) in different experiments. D-J spectroscopy has no mixing period (Wutrich, 1986). Reproduced with permission. 

Noroxohomoyessotoxin (noroxohomoYTX, 10, Eigure 13.1), a new addition to the class of YTXs, was reported in 2001. It was isolated from the digestive glands of mussels collected in 1998 from the northern Adriatic coast of Italy. The polycyclic skeletal structure was mainly assigned on the basis of homonuclear 2D NMR spectral data obtained from correlation spectroscopy (COSY) and HOmonuclear HArtmann HAhn (HOHAHA) experiments negative ion EAB MS/MS provided further valuable information to confirm the structure. 

There are probably, at present, about four homonuclear 2D NMR experiments in common usage for small molecules. These include COSY (Correlated SpectrospY) [46-48], TOCSY (TOtal Correlation SpectroscopY) [77-79], NOESY [35, 36, 49—51], and ROESY [35, 36, 52, 53], the latter two corresponding to nuclear Over-hauser and spin-locked Overhauser correlated experiments, respectively. Several less frequently employed homonuclear 2D experiments are also possible and include C— C [68, 69] double quantum spectroscopy [60—62] zero quantum spectroscopy [63—67], and others H. We will discuss the primary experiments in the category briefly in turn, and we will direct the reader interested in other homonuclear 2D variants to the appropriate literature. 

As a result of that study, the combination of covariance processing and NUS afforded a decrease in experimental time by a factor of two relative to linear sampling and covariance processing. It even shortened the total acquisition time by a factor of four as compared to conventionally sampled data and FT processing. Again, enhanced resolution and improved sensitivity were observed. The proof of concept was predicted to be amenable to other homonuclear 2D NMR experiments on liquid, aligned or solid samples. 

F. Zhang, L. Bmschweiler-Li, R. Bmeschweiler, High-resolution homonuclear 2D NMR of carbon-13 enriched metaboHtes and their mixtures, J. Magn. Reson. 225 (2012) 10. 

The similar NMR properties of F and as described in Table 24.1 means that most NMR experiments used for would also work to degree for F. With modern technologies, a large variety of multidimensional NMR experiments are feasible to probe the correlation within these three nuclei of fluoropolymers, of which the most basic are homonuclear 2D-NMR experiments discussed in Chapter 24.2.2. When... 

Gradient-enhanced homonuclear 2D NMR techniques, applied to D-mannose-containing oligosaccharides, provided improved intensity in correlations between protons in relatively short experimental times, especially whenVH,H values were small. ... 

R. Richarz and W. Ammann, Practical Tips for Homonuclear 2D-NMR Experiments, Varian Application Note No. Z-81, July 1981. 

Figure 22 Hypothetical homonuclear 2D-NMR spectta (a) COSY, (b) DQ-COSY, (c) TOCSY, and (d) NOESY.

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