Quadrupolar nucleus properties

Once an approximation to the wavefunction of a molecule has been found, it can be used to calculate the probable result of many physical measurements and hence to predict properties such as a molecular hexadecapole moment or the electric field gradient at a quadrupolar nucleus. For many workers in the field, this is the primary objective for performing quantum-mechanical calculations. But from... 

Vanadium-51 is a spin 7/2 nucleus, and consequently it has a quadrupole moment and is frequently referred to as a quadrupolar nucleus. The nuclear quadrupole moment is moderate in size, having a value of -0.052 x 10 2S m2. Vanadium-51 is about 40% as sensitive as protons toward NMR observation, and therefore spectra are generally easily obtained. The NMR spectroscopy of vanadium is influenced strongly by the quadrupolar properties, which derive from charge separation within the nucleus. The quadrupole moment interacts with its environment by means of electric field gradients within the electron cloud surrounding the nucleus. The electric field gradients arise from a nonspherical distribution of electron density about the... 

In early years of NMR, extensive studies of molecular dynamics were carried out using relaxation time measurements for spin 1/2 nuclei (mainly for 1H, 13C and 31P). However, difficulties associated with assignment of dipolar mechanisms and proper analysis of many-body dipole-dipole interactions for spin 1/2 nuclei have restricted their widespread application. Relaxation behaviour in the case of nuclei with spin greater than 1/2 on the other hand is mainly determined by the quadrupolar interaction and since the quadrupolar interaction is effectively a single nucleus property, few structural assumptions are required to analyse the relaxation behaviour. 

Figure 1. Representation of the properties of a nonquadrupolar and a quadrupolar nucleus. The charges around the nucleus represent those of its molecular environment. The electric field gradient tensor, qae, is expressed in the coordinate system of the molecule. Usually, the z-axis lies along the carbon-deuterium bond e is the charge on the electron, h is Planck s constant, and Q is the quadrupole moment. For axial symmetry, only q, is required to express the quadrupole coupling constant.

Hyperfine Parameters From a quantum chemical point of view, the quantity required for the determination of the nuclear quadrupole-coupling tensor is the electric field gradient at the quadrupolar nucleus. This is a first-order property which can be computed as either the first derivative of the energy with respect to the nuclear quadrupole moment or the expectation value of the corresponding (one-electron) operator... 

Quantum mechanical calculations of 33S nuclear quadrupole coupling constants are not an easy matter (not only for the 33S nucleus, but for all quadrupolar nuclei). Indeed, the electric field gradient is a typical core property, and it is difficult to find wave functions correctly describing the electronic distribution in close proximity to the nucleus. Moreover, in the case of 33S, the real importance of the Sternheimer shielding contribution has not been completely assessed, and in any case the Sternheimer effect is difficult to calculate. 

Because of its very different chemistry the only quadrupolar Group IV nucleus, Ge, is treated in a separate section. The nuclear properties of the six quadrupolar nuclides pertaining to main Groups III and IV are in Table VII. 

Methods based on the effects of the quadrupolar O nucleus (/ = f) and the 0 nucleus (7 = 0) on the P NMR spectral properties of the isotopically labeled P nucleus are now the only methods used to ascertain the configurations of tetrahedral phosphorus atoms in oxygen chiral phosphate esters. The chemical... 

The spectroscopy of multinuclear magnetic resonance in solution is one of the most important analytical methods in structural studies of transition metal hydride complexes. Among different nuclei, the proton plays the main role because H NMR provides a direct information about spectral properties of the hydride ligands. In addition the proton, being a non-quadrupolar and long-relaxing nucleus, gives rise to well-resolved NMR spectra which are very... 

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