Relativistic effects are often considered to be important largely for heavy elements. However, this is not the case for nuclear magnetic resonance (NMR) parameters. This is in part due to the fact that the nuclear magnetic shielding tensors and the indirect nuclear spin–spin coupling tensors are governed to a large extent by the electron density near the nucleus (outer core-inner valence electrons), but also due to the fact that magnetic interactions can be considered relativistic in nature.¹  The coupling between the electron spin and the orbital motion of the electrons through the spin–orbit operator allows for new interaction mechanisms between the nuclear magnetic moments or between the nuclear magnetic moments and an externally applied magnetic field. Many of these new interaction mechanisms also grow rapidly with increasing nuclear charge, making these relativistic effects particularly important for molecules containing heavy elements. It has been shown that the relativistic effects on the nuclear magnetic shielding tensors scale as Z^3.5 with respect to the nuclear charge Z.²  However, also light elements in the vicinity of heavy elements can display large relativistic effects. Even the lightest element, hydrogen, can display dramatic effects arising from relativity, with hydrogen iodide^3,4  and mercury hydride complexes^5,6  being prime examples. This effect is often referred to as the heavy-atom effect on light atoms (HALA),^3,7  to be contrasted with the effect of a heavy element on the NMR properties of the heavy element itself, the HAHA effect.