The shielding tensor. Part I: Understanding its symmetry properties

The shielding tensor and the chemical shift tensor are not necessarily symmetric, and in general they have both symmetric and antisymmetric parts. The antisymmetric part (not to be confused with the anisotropy of the symmetric part) does not give rise to an observable shift, even in the solid phase, but it does cause relaxation. The antisymmetric part of the shielding tensor can be considered in its corresponding axial vector form, and this allows the effect of symmetry at a nuclear site to be deduced easily. Instead of considering the complete symmetry point group at the nucleus, it is easier to consider only certain key elements of symmetry; this leads to four simple rules that determine the zero and nonzero components of the complete shielding tensor.