H Correlation

Figure 9-90. H correlation for various sizes of Raschig rings, Sc = Schmidt No. (Nsc)- Reproduced by permission of the American Institute of Chemical Engineers, Cornell, et al.. Chemical Engineering Progress, V. 56, No. 8 (1960) p. 68 all rights reserved.

COSY (H-H correlation spectroscopy) An important 2D experiment that allows us to identify the protons coupled to one another. 

A simple NMR technique, and arguably the most widely used and effective for hit validation, is the chemical shift perturbation method. In this approach, a reference spectrum of isotopically labeled target is recorded in absence and presence of a given test ligand (or a mixture of test ligands). Commonly, differences in chemical shift between free and bound protein target are observed in 2D [15N, 1H and/or 2D [13C, H] correlation spectra of a protein (or nucleic acid) upon titration of a ligand... 

Since phosphorus and protons are both abundant spin-1/ nuclei, it is simple to design an experiment in which we correlate protons and phosphorus rather than protons with themselves. The result of this experiment, a P,H correlation, is shown in Fig. 26. Again we have the 2D spectrum in the form of a central rectangle and two (previously recorded) ID spectra parallel to the axes. One is the proton spectrum, the other the phosphorus spectrum. The latter of course consists of a single line, and in the 2D spectrum we do not need to look for a diagonal as there cannot be one. 

Organic compounds almost always contain carbon and hydrogen, so that the C,H correlation is a key experiment in every structural determination. This experiment tells us which carbon signal corresponds to which proton signal, and the result for model compound 1 is shown in Fig. 27. 

Fig. 27 C,H correlation spectrum for compound 1 (set for directly bonded hydrogens, 200 MHz, 5% in CDC13, measurement time 60 min, inverse detection)...

Now, as in the H,H correlation, the actual 2D spectrum forms the central square, and the ID phosphorus spectra are depicted above and to one side of the square. There is a diagonal and there are cross peaks. 

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