Boron Isotope Effects in Fluorine NMR Spectra

In previous posts on this BLOG, examples of  ¹H/²H and ¹²C/¹³C isotope effects were discussed.  The figure below shows an example of a ¹⁰B/¹¹B isotope effect observed in the ¹⁹F NMR spectrum of tetrabutyl ammonium tetrafluorobarate.

The spectrum clearly shows two resonances separated by 0.05 ppm with an intensity ratio of approximately 20:80 corresponding to the natural abundances of  ¹⁰B and ¹¹B, respectively.  The low frequency resonance is due to ¹¹BF₄^-.  Since  ¹¹B is a spin I = 3/2 nuclide we observe a 1:1:1:1 quartet with J = 1.25 Hz corresponding to the one bond ¹⁹F - ¹¹B coupling.  The high frequency resonance is due to ¹⁰BF₄^-.  Since  ¹⁰B is a spin I = 3 nuclide we observe a very poorly resolved 1:1:1:1:1:1:1 septet with J ~ 0.4 Hz corresponding to the one bond ¹⁹F - ¹⁰B coupling.