The effects of electronic cloud of adjacent substituents on boron (Fig. ) is further evident from the upshifted signal of the boron in benzodiazaborine 4 in its B NMR spectrum in methanol-d 4 i.e. δ B 16.2 (Fig. ), relative to that obtained in acetonitrile-d 3 for benzodiazaborine 5 i.e. δ B 28.3 (Table ). Further support for the assertion that the aforementioned boronate esters 3) 'ring-closed' tetracyclic is provided by the upfield shift of δ-CH δ-CMe signals in NMR, relative to that observed for the C=O of their precursors i.e. 2-FPBA and 2-acetylphenylboronic acid (2-APBA), which suggests that the D 3h carbon of the formyl or acyl moieties, is now a T d centre, bonded to four substituents, and fully saturated. This arrangement brings the carboxyl moiety in the 'ring-open' structure in close proximity to the boronic acid so as to further cyclise, close the ring and form a 'tetracyclic caged' structure. This is in agreement with the observed IR frequencies i.e. ~ 1730-1710 cm -1 expected for esters (Table ), as the parent carboxyl moieties should resonate at lower frequencies i.e. ~ 1600-1550 cm -1 .