Editing Nuclear Overhauser effect (section)

{{Short description|Nuclear magnetic resonance spectroscopy effect}}
The '''nuclear Overhauser effect''' ('''NOE''') is the transfer of [[spin polarization|nuclear spin polarization]] from one population of [[Spin (physics)|spin-active]] nuclei (e.g. <sup>1</sup>H, <sup>13</sup>C, <sup>15</sup>N etc.) to another via [[Relaxation (NMR)|cross-relaxation]]. A phenomenological definition of the NOE in [[nuclear magnetic resonance spectroscopy]] (NMR) is the change in the integrated intensity (positive or negative) of one NMR resonance that occurs when another is saturated by irradiation with an [[Radio frequency|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 <sup>1</sup>H two-dimensional NOE spectroscopy (NOESY) experiment and its extensions are important tools to identify stereochemistry of proteins and other biomolecules in solution, whereas in solid form crystal x-ray diffraction typically used to identify stereochemistry.<ref name="Noggle">{{cite book
 |last1=Noggle
 |first1=Joseph H.
 |last2=Schirmer
 |first2=Roger E.
 |year=1971
 |title=The Nuclear Overhauser Effect: Chemical Applications
 |url=https://archive.org/details/nuclearoverhause0000nogg
 |url-access=registration
 |publisher=Academic Press
 |page= <!-- or pages= -->|isbn=9780125206501
 }}</ref><ref name="Neuhaus">{{cite book
 |last1=Neuhaus
 |first1=David
 |last2=Williamson
 |first2=Michael P.
 |year=2000
 |title=The Nuclear Overhauser Effect in Structural and Conformational Analysis, 2nd ed.
 |publisher=Wiley-VCH
 |page= <!-- or pages= -->}}</ref><ref name="Claridge">{{cite book
 |last1=Claridge
 |first1=Timothy D.W.
 |year=2016
 |title=High Resolution NMR Techniques in Organic Chemistry, 3rd ed.
 |publisher=Elsevier
 |page=315 <!-- or pages= -->
 |isbn= 978-0080999869}}</ref> The heteronuclear NOE is particularly important in <sup>13</sup>C NMR spectroscopy to identify carbons bonded to protons, to provide polarization enhancements to such carbons to increase signal-to-noise, and to ascertain the extent the relaxation of these carbons is controlled by the dipole-dipole relaxation mechanism.<ref>{{Cite journal
|last1=Kulhmann
|first1=Karl F.
|last2=Grant
|first2=David M.
|last3=Harris
|first3=Robin K.
|year=1970
|title=Nuclear Overhauser Effects and <sup>13</sup>C Relaxation Times in <sup>13</sup>C &lbrace;H&rbrace; Double Resonance Spectra
|journal=Journal of Chemical Physics
|volume=52
|issue=7
|pages=3439–3448
|doi=10.1063/1.1673508}}</ref>