Whilst the aromaticity of diazaborines can play a crucial role in the observed data, as illustrated above (Eq. III) the electronic cloud of heteroatoms with available lone pairs adjacent to the boron centre in question can account for the aforementioned large upfield shift of almost 20 ppm in their B NMR spectra (Fig. ). In view of the above, it is conceivable that the boronate esters are tetracyclic and 'ring-closed', as if they were 'ring-open' and tricyclic, the thus C 3h boron species, would be less shielded, and would absorb at about the expected field in B NMR, just like that of 2-FPBA with similar chemical environment and shielding effects (Fig. ).