Measuring coupling constants shielding

W. Makulski and M. Wilczek, Nuclear magnetic shielding and indirect spin-spin coupling constants in cyclopropane. Gaseous and liquid NMR measurements. Polish J. Chem., 2006, 80(7), 1055-1060. 

NMR shieldings at the oxygen can also be obtained for mineral systems and are calculated to show the same angular trends as for silicon (Tossell and Lazzeretti, 1988a). However, O is a quadrupolar nuclide (i.e., with a nonzero quadrupole moment), and its nuclear quadrupole coupling constant is thus an easier to measure quantity and, probably, one of more interest. When few data on the O NMR of silicates existed, Janes and Oldfield (1986) noted that different bonding models for silicates predicted different dependence of q° upon Si-O-Si angle. In particular. 

The NMR characteristics of phosphirenes once again include a strong upfield shift of the 31P resonance and very high J (C—P) coupling constants. The parameters for a representative phos-phirene are listed in Table 4. The 31P magnetic shielding tensor components of phosphirene (3) have also been measured <87CPL(136)224>. 

Since the short relaxation times associated with a quadrupolar nucleus drastically reduce the time delay to be applied in an NMR experiment between two pulses, measuring times are short or, in other words, distinct NMR signals can often be detected with a limited time spent down to micromolar concentrations. Along with this apparent advantage, quadrupolar nuclei provide information in addition to the classical parameters chemical shift (or shielding) and nuclear spin-spin coupling constants. Variations in linewidths for quadrupolar nuclei are another sensitive quantity allowing for the evaluation of the electronic and the steric situation in the first coordination sphere of a vanadium compound, its periphery, its (local) symmetry and its interaction with the matrix, i.e. counter-ions, solvent molecules and other constituents present in solution. 

In this Hamiltonian, the a/ are the shieldings, or chemical shifts, of the nuclei, J / the indirect spin-spin coupling constants between pairs of nuclei, IZi the z component of the spin operator 7, y the gyromagnetic ratic and H0 the strength of the static applied field. Within the experimental accuracy of measurements achieved thus far, no additional terms are required in the Hamiltonian to attain an exact fit of theoretical and calcu-... 

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