The Cinderella Nuclei

Abstract

The chapter discusses the cinderella nuclei. The sensitivity of these nuclei is low. All the nuclei are less sensitive than 13 C, with 187 Os having only 1/877 the sensitivity of 13 C. They resonate at low frequency and the purchase of additional probe(s) had to be justified. With the development of nuclear magnetic resonance (NMR) technique, these nuclei can now be readily observed. Many of the early observations of these insensitive nuclei were performed, using internuclear double resonance (INDOR). This technique required coupling to the insensitive nuclei and spectra was produced, either by observing the sensitive nucleus and decoupling the insensitive nucleus or by using a triple resonance relay, where sensitive nucleus is observed, a less sensitive nucleus is irradiated and the insensitive nucleus in irradiated. This technique uses continuous-wave observation. It is as sensitive as the observed nucleus, but is difficult to use with signal averaging. INDOR became disused, as continuous-wave NMR spectrometers were displaced by Fourier-transform NMR spectrometers that are not amenable to this technique, but are preferable for most other NMR experiments. Direct observation of these insensitive nuclei is difficult. The observation of these nuclei by Fourier-transform NMR spectroscopy has become much easier over the past few years, with the development of inverse detection methods, analogous to INDOR. The chapter explains that the chemical shifts of cinderella nuclei are dominated by the paramagnetic term, σ p .