S nuclear quadrupole coupling constants

While S relaxation behaviour can provide interesting information about interactions in solution, nuclear quadrupole coupling constants are a very sensitive probe in the study of the electronic distribution around the sulphur nucleus. 

Expressing qzz in Equation (4) as a function of valence orbital populations, the dependence of 33S y on the electronic distribution around the nucleus is given by the following relationship 81 

The distortion of closed shell electrons can be very significant in the case of charged species. The Stemheimer antishielding factor has been determined for sp3d2 hybridized sulphur by evaluation of the ion-water contribution to the 33S relaxation rate in aqueous SO4, 83 The value found (y, — —43.9) is in good agreement with the value reported for S2 (yrf, — —52.2) in the crystalline state.84 

From relaxation times or line widths in liquids (Equation (3)), it is possible to determine the term ) (l+r]Z/3) provided that correlation time values are known. The absolute values of x can be obtained if the asymmetry parameter t] is known, or they can be deduced using symmetry considerations regarding the electronic distribution around the nucleus. 

The determination of correlation times requires particular attention and is not a problem that can be easily resolved. It is necessary to consider not only the overall molecular tumbling, but also internal rotation motions, which can modulate the interaction between the nuclear quadrupole moment and the electric field gradient. In any case, it must be considered that % depends on the square root of and, even if in most cases it is not possible to measure or calculate precise values of t , the uncertainties introduced in the values of x may often be accepted. 

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Ab initio calculations of S nuclear quadrupole coupling constants (NQCC) of some 1,2-dithioles... 

Ab initio calculations of S nuclear quadrupole coupling constants have been carried out on a variety of sulfur compounds using a TZVP basis set <92ZN(A)203>. The equilibrium geometric parameters calculated by this method follows the trend of the other ab initio methods and the values are within the acceptable limits. 

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