Nuclear Overhauser enhancement spectra

In decoupling the methyl protons, the NOE difference spectrum shows a nuclear Overhauser enhancement on the cyclopropane proton at = 1.60 and on the terminal vinyl proton with trans coupling at <5// = 5.05 and, because of the geminal coupling, a negative NOE on the other terminal proton at Sh= 4.87. This confirms the trans configuration G. In the cis isomer H no NOE would be expected for the cyclopropane proton, but one would be expected for the alkenyl-// in the a-position indicated by arrows in H. 

Little difference was noted when peak heights were used. The error in the T data is less than + 10%. Nuclear Overhauser enhancement factors (q) were obtained by measuring the integrated intensity of peaks in a difference spectrum from one with enhancement minus one with no enhancement and dividing that value by the integral from the one with no enhancement i.e. n ( nOe no nOe / (I nOe" Accuracy should be 10% or better. Linewidtns were measured at half heights, and chemical shifts are relative to TMS. 

NMR spectrum depends on the type of starch (amylose-to-amylopectin ratio) and is associated with the numbers of carbon atoms in the branching points and thermal glucose units. Tables X and XI present 13C spin-lattice relaxation times (Tus) and nuclear Overhauser enhancement (n.O.e) for l3C nuclei of starches of various origins. Figure 21 shows H NMR spectra of amylose and a high-amylopectin waxy sorghum starch. 

Signals can also be correlated through Nuclear Overhauser Enhancement (NOESY) [31], which gives a spectrum similar to COSY with peaks due to both NOE and scalar coupling. NOESY spectra, therefore, must be interpreted in conjunction with a COSY spectrum. Careful choice of the pulse interval in which the NOE develops is necessary and may require several experiments to find the optimum. 

Figure 1.2.13 (a) Partial 400 MHz IH-NMR spectrum of the methine protons of testosterone. A hopeless case for assignment, (b) Decoupling and nuclear Overhauser enhancement effects can be used to disect the multiline, one-dimensional spectrum into a variety of two-dimensional spectra. Assignment of signals to individual hydrogen atoms can thus be achieved. (From Sanders and Hunter, 1993.)... 

One of the most important uses of distance geometry is for deriving conformations that are consistent with experimental distance information, especially distances obtained from NMR experiments. The NMR spectroscopist has at his or her disposal a range of experiments that can provide a wealth of information about the conformation of a molecule. Two of the most commonly used NMR experiments that provide such conformationally dependent information are the 2D-NOESY (nuclear Overhauser enhancement spectroscopy) and the 2D-COSY (correlated spectroscopy) experiments [Derome 1987]. NOESY provides information about the distances between atoms which are close together in space but may be separated by many bonds. The strength of the NOESY signal is inversely proportional to the sixth power of the distance and so by analysing the nuclear Overhauser spectrum it is possible... 

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