High-resolution NMR spectra

High Resolution NMR Spectra Catalog, Vol. 2, Spectrum No. 464, Vadan Assoc., Palo Alto, Calif., 1963. 

With the new very high resolution NMR spectra, it should be a simple matter to assign configurations to other difficult cyclitols or carbohydrates, for example, the numerous still undiscovered isomers of 6-bromo, 6-chloro, and 6-iodoquercitol (20 diastereomers predicted for each). 

P. A. Keifer 1998, (New methods for obtaining high resolution NMR spectra of solid-phase-synthesis resins, natural products, and solution-state combinatorial chemistry libraries), Drugs Future 23, 301-307. 

Unlike high-resolution NMR spectra of bulk solutions where NMR linewidths well below 1 Hz can be obtained routinely, NMR spectra of liquids permeating porous solids in most cases will not exhibit such a high spectral resolution. First of all, the interaction of liquid phase molecules with pore walls of the catalyst and rapid diffusion-driven intrapore transport will lead to a pronounced homogeneous broadening of the observed NMR lines. Smaller pore sizes and the presence of paramagnetic impurities in the solid material usually aggravate the situation and thus should be avoided. Another reason why NMR spectra of liquids in porous... 

Varian Associates, High Resolution NMR Spectra Catalogue, Varian, Palo Alto, CA (1962/3), Vol. 2. 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

Each of these tin atoms acts as a Lewis acid, with two neighboring nitrogen atoms functioning as electron donors. The ten-membered ring folds up to generate a four-membered cycle bridged at the 1,3- and 2,4-positions. The structure, which can easily be deduced from high-resolution NMR spectra, is displayed in Fig. 14. 

In 2006 Wimperis et al. proposed a method called satellite transitions acquired in real time by MAS (STARTMAS) [142, 202], which allows for the real-time acquisition of high-resolution NMR spectra of spin-3/2 nuclei under MAS. This method combines a train of pulses, similar to CPMG [109, 110], with sample rotation at the magic angle to refocus the quadrupolar broadening in a series of echoes, while allowing the isotropic quadrupolar shift and chemical shift to evolve. 

Fig High-resolution NMR spectra of biophenolA polycarbonate in deutrochloroform solution showing the effect of frequency on resolution. 

With TROSY, CRIPT and CRINEPT, high-resolution NMR spectra of macromolecules with masses of one to several hundred thousand Daltons can be recorded [3, 26, 35] (Figs. 10.1 and 10.6). Sequence-specific NMR assignments for large structures have already been obtained (Fig. 10.5), and TROSY-based NOESY experiments [12, 16, 31, 32] for the collection of structural constraints are also available. Practical applications for... 

High resolution NMR spectra very often exhibit signals as multiplets, invariably showing a more or less symmetrical appearance. 

Determinations of epr fine structure and paramagnetic susceptibilities are most often used. For characterization of higher spin orders, neutron diffraction and other physical methods may be useful. On the other hand, a successful measurement of normal high-resolution nmr spectra would serve as good evidence for singlet ground states of the chemical entities at issue. 

As the TieS lengthen and l/Tie (s ) approaches the size of the electron—nuclear interaction, considerable NMR line broadening can occur, and it may not be possible to acquire high-resolution NMR spectra under these conditions. The effect of Tie on the nuclear relaxation times is discussed in more detail in ref 22. Large hyperfine constants are observed (of many MHz) when the nuclear and electronic spins are on the same atom. For example, a hyperfine constant A/h of —324 MHz was measured by electron... 

When high-resolution NMR spectra have to be recorded of a polymeric sample, one has to recognize that polymer solutions are in general highly viscous. To prevent excessive signal broadening caused by this restricted mobility of the solution, polymer solutions for NMR studies have to be highly diluted (approx. 

Bhacca, Johnson, Shoolery, Catalogue of High-Resolution NMR Spectra, Varian Associates, Palo Alto, 1962. 

The association, or interaction, of one molecule with a second type of molecule may be expected to affect their relative molecular motion. In particular cases the motion of a segment, or part of a molecule, may be more affected by the mutual interaction than other parts of that molecule. If this is the case, differential broadening of lines in the high resolution NMR spectra can occur, and information about the mode of interaction can sometimes be obtained (II). 

High resolution proton magnetic resonance (PMR) spectra were recorded on a Perkin-Elmer R-10, 60-megacycle per second spectrometer fitted with a decoupling unit, a temperature probe, and a computer averaging attachment. Unless specified otherwise, spectra were obtained at 33.5°C. Chemical shifts in the high resolution NMR spectra are expressed as usual in parts per million relative to the protons of tetra-methylsilane at 10 p.p.m. (t scale). 

Hand-shaken dispersions of phospholipids thus may be a more reasonable choice for comparison with membranes, and except in rare cases of highly unsaturated systems the high resolution NMR spectra of such dispersions do not exhibit high resolution proton absorption. Hence, for most membranes, NMR can indicate immobilization of fatty acid chains but not whether chains are immobilized by binding onto proteins or by tight packing into bilayers. Broad line NMR may be useful, especially when a phase transition is present. 

Fig. 21. Standard 100 MHz high resolution NMR spectra of crosslinked polystyrene equilibrium swollen in CCld 65 °C. (a) experimental, (a ) calculated (adapted from Ref.113))...

P. Diehl, H. Kellerhals, and E. Lustig NMR, Basic Principles and Progress, Vol. 6, Computer Assistance in the Analysis of High-Resolution NMR-Spectra. Springer, Berlin, Heidelberg, New York 1972. 

LH Keith, AL Alford. The high resolution NMR spectra of pesticides. HI. The Carbamates. J Assoc Off Anal Chem 53 157-179, 1970. 

An important characteristic of the cubic mesophases, either non-amphiphilic or amphiphilic, is that because of the fairly free thermal rotational motions of their constituent units, they typically give high resolution NMR spectra. In this respect they behave like amorphous liquids and quite differently from conventional solids or from mesophases such as Mi, M2, or G in which rotation of the units is more severely restricted. 

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