Background‐free solution boron NMR spectroscopy

The appearance of background signals arising from the NMR probe and tube is a well‐known problem of boron NMR spectroscopy. Background suppression may be achieved by using DEPTH, which increases the signal‐to‐background (S/B) ratio. Although, the quality of such spectra is often adequate, but in the case of rapid relaxation broadened resonances ( T 1 < 1 ms), the residual background signals may still hamper the interpretation of the spectra. It was observed that the background signals are practically invisible in solution 10 B NMR. The unusual isotopic effect on the (S/B) ratio was interpreted as an inherent consequence of the integer versus half‐integer spin of 10 B and 11 B, respectively. The practicability of 10/11 B NMR was compared for a selected set of boron compounds covering the typical range of (S/B) ratio. The application of 11 B is more favourable than 10 B as long as it is possible to achieve the desired spectral quality by using DEPTH. Otherwise, the ‘background‐free’ appearance of 10 B NMR spectra makes 10 B a reasonable alternative of 11 B DEPTH. This was found typical for compounds having relaxation broadened resonances. The variable temperature (VT) NMR study of an adduct formation process was also presented here as an example of the advantage of 10 B over 11 B. Copyright © 2012 John Wiley & Sons, Ltd.