Systems magnetic resonance nuclei

Since this dipolar interaction remains in isotropic media as similarly found for the contact shift (see sect. 2.1), it is often termed as the pseudo-contact shift. For the general case of a complex possessing an anisotropic magnetic susceptibility tensor, Kemple et al. (1988) show that the pseudo-contact shift spherical coordinates of the resonating nucleus in an arbitrary axes system with the lanthanide metal ion i (III) located at the origin (fig. 1)... 

The situation has been elucidated in a series of recent papers Magnetic resonance in systems with equivalent spin-1/2 nuclides. 13 1 38 39 These works deal with EPR examples, that is each with an impaired electron exposed to a set of n equivalent 1=1/2 nuclei. For our present purpose, we can deem the electron to have been replaced by some spin-bearing nucleus to be examined by NMR. 

Nuclear Magnetic Resonance. Ziircher s massive compilation of chemical shifts of 18-H and 19-H signals, and increments produced by structural features in the steroid nucleus, is augmented by the publication of similar data for 344 steroids obtained by microbiological hydroxylations, and subsequent transformations. The compounds are mainly 5a-androstane derivatives, and include hydroxy- and oxo-functions at almost all the ring positions, as well as their derivatives and polyfunctional compounds. Solvent shifts are also reported. A set of diagrams illustrates the profiles and chemical shifts of signals due to methine protons in the C/fOH system at all the main steroid positions. ... 

If one wishes to extract stereochemical information about substrates in solution from the data obtained in the NMR experiments, two physical-mathematical models are available. For shifts induced by a dipolar (pseudocontact) mechanism, the McConnell-Robertson equation (Equation 1) (28, 29)—where r, i, and are the spherical polar coordinates of the ith resonating nucleus in the coordinate system of the principal magnetic axes—relates the direction and magnitude of the shift to the geometry of the substrate-chelate complex. If the substrate-chelate... 

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