Features of signals from protons of alkyl group on boron atom in PMR spectra of 1,3,2-oxazaborinanes

It has been shown that the signal from isopropyl-group protons in the PMR spectra of 2-isopropyl-1,3,2-oxazaborinanes degenerates into a singlet; but the protons of the gem-dimethyl groups and the methylene link in an isobutyl substituent on the boron atom, where a chiral center is present in the molecule, may manifest anisochronicity. In the latter case, δδ is determined by the character of the solvent, the temperature, and the contribution of the conformation with a flexible form.