Nuclear magnetic resonance spectroscopy theoretical considerations

In this review recent theoretical developments which enable quantitative measures of molecular orientation in polymers to be obtained from infra-red and Raman spectroscopy and nuclear magnetic resonance have been discussed in some detail. Although this is clearly a subject of some complexity, it has been possible to show that the systematic application of these techniques to polyethylene terephthalate and polytetramethylene terephthalate can provide unique information of considerable value. This information can be used on the one hand to gain an understanding of the mechanisms of deformation, and on the other to provide a structural understanding of physical properties, especially mechanical properties. 

To develop a unifying view of iron center catalysis, properties of the iron center in individual enzymes must be determined. Obviously, the definitive solution for the structure is atomic resolution of the active enzyme and postulated intermediates determined by diffraction or nuclear magnetic resonance (NMR) spectroscopy. Just as obviously, these methods are limited by enormous time, effort, and instrumentation requirements as well as by practical and theoretical considerations. This point is emphasized by the paucity of available protein structures. In addition to the strictly structural details of the iron center, chemical and physical properties are required and, in some cases, these results augment diffraction or NMR structural studies. Discussed below are a few of the more common processes by which this information is obtained. 

Since the publication of CHEC-II(1996), there has been little advance, with respect to ring-fused oxiranes, in experimental structural methods (e.g., nuclear magnetic resonance (NMR), ultraviolet (UV), and Raman spectroscopy). However, there has been considerable interest in the use of theoretical computational studies to probe structural and reactivity issues, particularly with regard to highly labile oxiranes fused to small rings. 

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