Chemical Shifts of Other Elements

We do not have the space here to discuss the chemical shifts of all of the many elements that have been smdied by NMR, but some comments must be made on C, F and P as they are so widely used. We will also mention Se and Te as they are examples of typical heavier non-metals, and Mn and Pt as they are commonly-studied transition metals. 

Some typical ranges and some representative examples of chemical shifts. 

1975 Oldenbourg Verlag. (b) Dependence of P NMR chemical shifts on the degree of substitution of Cl and Br atoms by F atoms. Redrawn with permission from [13]. Copyright 1968 Taylor Francis. 

The chemical shifts of F cover a wider range of some 900 ppm, and are not easy to interpret, as they are sensitive to the electronegativity and oxidation states of the neighboring groups, to stereochemistry. 

Representation of P chemical shifts of phosphines with H, SiHs and PF2 substituents. The regularity of changes enables the chemical shifts of the unknown compounds P(Pp2)3, PH(Pp2)2 and P(Pp2)2(SiH3) to be predicted. 

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Ab-initio calculations are particularly usefiil for the prediction of chemical shifts of unusual species". In this context unusual species" means chemical entities that are not frequently found in the available large databases of chemical shifts, e.g., charged intermediates of reactions, radicals, and structures containing elements other than H, C, O, N, S, P, halogens, and a few common metals. 

HETCOR (Section 13 19) A 2D NMR technique that correlates the H chemical shift of a proton to the chemical shift of the carbon to which it is attached HETCOR stands for heteronuclear chemical shift correlation Heteroatom (Section 1 7) An atom in an organic molecule that IS neither carbon nor hydrogen Heterocyclic compound (Section 3 15) Cyclic compound in which one or more of the atoms in the nng are elements other than carbon Heterocyclic compounds may or may not be aromatic... 

In addition to the influence of neighbors on 29Si chemical shifts, the geometrical effects (such as Si-O-T angles) already described above are also evident of mixed frameworks with elements other than Si on tetrahedral positions. This is reflected by the broadness of the bars shown in Fig. 1. Multinuclear NMR investigations on a large set of sodalite structures with various framework compositions show that T-O-T bond angle (T = Si, Al, Ga) and dTT distance chemical shift dependences exist, and mutual correlations between chemical shift of these NMR nuclei can be observed [68],... 

Fig. 5.4 depicts some results obtained in the first stages (high nuclearity complexes formation) of the synthesis in xylene solvent which leads to the formation of nanostructured powders, RuxSey, from tris-ruthenium dodeca-carbonyl (Ru3(CO)i2) and elemental selenium dissolved in an organic solvent (xylene). After 40 minutes of reaction, l3C-NMR spectrum (Fig. 5.4 (c)) puts in evidence the formation of a new polynuclear chemical precursor with a chemical shift 8 of 198.89 ppm (i.e., Ru4Se2(CO)n)- Selenium takes part in the coordination sphere. The peak intensity with the chemical shift of 199.67 ppm, corresponds to the initial chemical precursor which decreases as a function of the synthesis reaction time (Fig. 5.4(a)). Other chemical shifts (with minor peak intensities) on both sides of the 13C-NMR spectrum, which put in evidence the complex interplay of the reaction, are also observed. 

We have attempted in this brief chapter to introduce a few other useful nuclei and some examples of their spectra. The emphasis in this chapter is to utilize these spectra in combination with other spectra, especially other forms of NMR. We must concede that it is neither possible nor desirable to become experts on chemical shifts of these (or other) nuclei and their coupling constants. In making this concession, we can be comfortable with these four nuclei, and furthermore, we can easily broaden our outlook to other elements throughout the periodic table. 

For these complexes, the isotropic and 15N chemical shifts and the 15N chemical shift tensor elements were measured as a function of the hydrogen bond geometry. Lineshape simulations of the static powder 15N NMR spectra revealed the dipolar 2H-15N couplings and hence the corresponding distances. The results revealed several correlations between hydrogen bond geometry and NMR parameters which were analysed in terms of the valence bond order model. It was shown that the isotropic 15N chemical shifts of collidine and other pyridines depend in a characteristic way on the N-H distance. A correlation of the and 15N... 

While complete X-ray analysis will establish the structure in the solid state, it is useful to have NMR data on the solution state that illustrate the increase of the coordination number of silicon. It would seem that NMR spectroscopy of nuclei participating directly in donor-acceptor interaction is especially important in investigating silicon compounds with an expanded coordination sphere. This requires the use of Si NMR spectroscopy since the electron shell of the silicon atom, the bond angles and lenghts are strongly affected upon complexation. Valuable information could also be obtained with by " N, N, 0, F NMR data since these elements act as donors. Chemical shifts of nuclei other than hydrogen are determined by various factors and not yet understood well anough to provide easily applied correlations of other physical properties of the molecules. 

The principal limitation in identification of chemical states has been the fact that photoelectron line energy is a one parameter system. Moreover, chemical shifts in some elements are very small for example those of Zn, Ag, Cd, In, and the alkali metals and alkaline earths encompass ranges of less than two electron volts, so that for these elements this technique has little use. Clearly there is much incentive to find other... 

Chemical shifts in the line energies of the Cls, Nls, 01s, FIs, and the strong photoelectron lines of other elements have been useful for the identification of chemical states. Application is limited, however, because only one property is variable and with some elements the range in chemical shifts is very small. 

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