The Nuclear Overhauser Effect and Associated Techniques

Whereas spin decoupling, COSY and TOCSY techniques are used to establish connectivities between protons through bonds, techniques that make use of the nuclear Overhauser effect (NOE), such as 1-D NOE and NOESY, 1- and 2-D GOESY, 1- and 2-D ROESY, can establish connectivities through space. Before looking at these techniques in detail, it s worth spending a little time considering the NOE phenomenon itself - in a nonmathematical manner, of course  

The ability to devise experiments that can make use of the NOE gives us massively powerful tools which can be used to crack all manner of problems. For example, they can be used in the more trivial sense, as an assignment aid and to tackle problems of positional isomerism. But the area where NOE experiments really come into their own by offering information that no other NMR techniques can offer, is in the field of stereochemistry. Is this group up or down Could this centre have epimerized An NOE experiment could be just what you need. 

As an example of how useful an NOE experiment can be, consider the structures in Structure 8.1 

In this example, both the -CH2- and the -CH3 would be excellent targets for irradiation and we would recommend making use of both of them. A brief inspection of the 1-D spectrum (Spectrum 8.3) is enough to confirm that the compound does have both substituents on one of the rings as four protons can easily be observed as one continuous spin system (8.13, 7.85, 7.6 and 7.48 ppm) whilst the remaining 

Spectrum 8.3 Naphthalene substituted with -CH3 and -CH2-CI groups and expansion. 

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