Magnetic-activated

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

Coupling constants are routinely used to determine the side-chain conformation of amino acids in peptides and proteins. Whereas proteins nowadays are almost exclusively studied as C- and N-labeled isotopomers, peptides usually have these isotopes in natural abundance, i.e. the magnetically active heteronuclei are highly diluted. Most amino acids contain a methylene group at the ji-position for which the X angle is determined by the conformation of the Ca—Cp bond. Two vicinal Jhh coupling constants can be measured Ha to and H to Usually... 

Metallophosphazenes are a new type of macromolecule designed to bridge the gap between polymers and metals. Although still at an exploratory stage of laboratory development, they may provide access to electronically-conducting polymers, magnetically-active polymers, macromolecular catalysts, electrode mediator systems, or polymers crosslinked by metal atoms. 

Tin is an unusual element in that it has three magnetically active isotopes, all spin-Vi. However, tin-115 has a natural abundance of only 0.35%, and is never studied. The other two, tin-117 and tin-119, occur in similar amounts (7.61 and 8.58% respectively). Spectra of the latter are normally recorded, as it is about 25% stronger. Tetramethyltin is taken as the zero-point, and the total chemical shift range is about 3000 ppm. 

Platinum-195 is the only magnetically active isotope of platinum, the natural abundance being 33.8%. The shift of a saturated solution of K2PtCl6 is in D20 defined as zero ppm. The total chemical shift range is huge, about 13,000 ppm (from -6000 to +7000 ppm ). 

Likewise, the original proton polarization can be transferred to other magnetically active heteronuclei, notably to 13C, 15N, 19F, 29Si, 31P or appropriate isotopes of various transition metals. This is especially attractive because of the frequently low sensitivity of many heteronuclei, in particular of those with low magnetic moments [8]. 

Likewise, the initial proton polarization may be transferred to other magnetically active heteronuclei, most attractively to those associated with a low y-value of their nucleus (i.e., to 15N, 29Si), and similarly difficult ones, using heteroatom PHIP at low magnetic fields [8, 45]. 

So far we have studied the NMR ( or PMR) spectroscopy and its applications. In recent years a new technique called the 13C - NMR or CMR technique has been developed. 12C nucleus is not magnetically active because its / = 0 and does not give any NMR signal. 13C like H has a spin 1... 

It is interesting to note that 12C nucleus is not magnetically active (spin quantum number I = 0),... 

A general comment on the use of the empirical correlation between Si and Sn NMR (and likewise on C/ Si or Sn/ Pb NMR) chemical shifts is in order. The basis for this correlation is that the paramagnetic term Op dominates the chemical shift. According to Ramsay s theory, Op is proportional to the reciprocal energy difference h.E between the magnetically active orbitals and proportional to the expectation value for the electron radii (r )np- Thus, a linear correlation between the 5 Si and 8 Sn implies that the ratio of both determining factors of Op is constant for the all compounds of interest. In particular, it is not clear, however, if the ratio for tetravalent silicon and tin compounds is the same as for trivalent silicon and tin compounds. Therefore, the extension of a correlation based exclusively on the... 

Chemical shifts of magnetically active nuclei, such as [79MI171], Vicinal and geminal scalar H,H and H,C coupling constants Line widths of proton resonances of tertiary protons... 

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