Nuclear overhauser experiment

NOE Nuclear Overhauser experiment. Experiment designed to capitalise on the above. Such experiments (and related techniques, e.g., NOESY, etc.) are extremely useful for solving stereochemical problems by spatially relating groups or atoms to each other. 

ROESY Rotating-frame Overhauser effect spectroscopy. A variation (one and two dimensional) on the nuclear Overhauser experiment (NOE). The techniques have the advantage of being applicable for all sizes of molecule. See Laboratory frame model. 

The observed rc-face differentiation of the electrophilic animation process was rationalized by the authors [14b]. NMR Nuclear Overhauser experiments agree with the ( -configuration of the O-silyl ketene acetals 35 and with a j-yn-periplanar disposition of the C -OSi and C2-Ha bonds. Electrophiles E+ , such as Lewis acids-co-ordinated DTBAD, attack 35 preferentially from the less hindered C(a)-Si (back) face (Scheme 17). 

Figure 6-31 The enhancement factor t as a function of the effective correlation lime Tc for the standard nuclear Overhauser experiment (NOE) and for the spin-lock, or rotating-coordinate, (ROE) variant. The curves were calculated for an interproton distance of 2.0 A and a spectrometer frequency of 500 MHz, (Reproduced from F. J. M. van de Ven, Multidimensional NMR in Liquids, VCH, New York,...

States DJ, Haberkom RA, Ruben DJ (1982) A two-dimensional nuclear Overhauser experiment with pure absorption phase in four quadrants. J Magn Reson 48 286-292... 

A ID nuclear overhauser experiment (NOE) (Gaggelli and Valensin, 1993) is an important and valuable variation on the simple ID NMR experiment that provides spatial relationship between each nucleus in the structure. Coupling constants observed in a ID H NMR spectra provide connectivity for directly bonded nuclei whereas, a ID NOE experiment identifies nuclei that are close in space (<6A). Briefly, a ID NOE experiment requires the addition of a second lowpowered rf pulse that selectively saturates a specific peak in the NMR spectrum. The saturated peak becomes a null in the spectrum and any other nuclei that are coupled through space via a dipole-dipole interaction to the saturated peak will experience a change in peak intensity. A ID NOE experiment requires collecting two NMR spectra, with and without saturation, to monitor changes in peak intensity. A summary of common ID NMR experiments and their applications are listed in Table 12.6. 

Nuclear Overhauser experiments on purified synthetic 6 confirmed that it did have the E,E,E,E configuration. Irradiation at an olefinic methyl or methylene causes significant enhancement of an olefinic proton that is cis to it but not for one that is trans (5,11). Proton assignments were made based on double irradiation... 

The structures of the isomeric retinol derivatives (36), (37), and (38) were also established on the basis of nuclear Overhauser experiments (Chandraratna and... 

The structures of (679) and (680) were assigned unambiguously by means of a nuclear Overhauser experiment, because only one of the two compounds, the cis retinoid (680), exhibited an increase in intensity for the signal of the olefmic proton when the compound was irradiated at the frequency of the olefinic methyl signal. The carboxylate (679) was hydrolyzed to the carboxylic acid (20) under standard conditions. 

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