It is difficult to overemphasize the importance of magnetic resonance techniques in chemistry. Experimental spectra can usually be successfully interpreted empirically, but more difficult cases require a prediction based on the electronic structure. In the last 25 years the calculation of magnetic resonance parameters from first principles has become a powerful research tool that can significantly enhance the utility of magnetic resonance techniques when empirical interpretations are insufficient. This can be crucial even for NMR spectra of organic molecules, where the interpretations are the simplest and where empirical material has been collected for half a century
