page_title: Nuclear Overhauser effect
section_title: Examples of nuclear Overhauser effect
hierarchical_section_title: Nuclear Overhauser effect / Examples of nuclear Overhauser effect
caption_attribution_description: English: Example of Nuclear Overhauser effect
context_page_description: The nuclear Overhauser effect is the transfer of nuclear spin polarization from one population of spin-active nuclei to another via cross-relaxation. A phenomenological definition of the NOE in nuclear magnetic resonance spectroscopy is the change in the integrated intensity of one NMR resonance that occurs when another is saturated by irradiation with an RF field. The change in resonance intensity of a nucleus is a consequence of the nucleus being close in space to those directly affected by the RF perturbation.
  The NOE is particularly important in the assignment of NMR resonances, and the elucidation and confirmation of the structures or configurations of organic and biological molecules. The two-dimensional NOE experiment is an important tool to identify stereochemistry of proteins and other biomolecules in solution, whereas in solid form crystal x-ray diffraction must be used to identify the stereochemistry.
context_section_description: The figure (top) displays how Nuclear Overhauser Effect Spectroscopy can elucidate the structure of a switchable compound. In this example, the proton designated as {H} shows two different sets of NOEs depending on the isomerization state (cis or trans) of the switchable azo groups. In the trans state proton {H} is far from the phenyl group showing blue coloured NOEs; while the cis state holds proton {H} in the vicinity of the phenyl group resulting in the emergence of new NOEs (show in red).
  Another example (bottom) where application where the NOE is useful to assign resonances and determine configuration is polysaccharides.  For instance, complex glucans possess a multitude of overlapping signals, especially in a proton spectrum. Therefore, it is advantageous to utilize 2D NMR experiments including NOESY for the assignment of signals. See, for example, NOE of carbohydrates.
caption: Nuclear Overhauser effect[19]
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