Conformational energy of the methy group at the C(5) atom in 1,3,2-oxazaborinates

The method of³H and¹³C NMR spectroscopy was utilized to determine the conformational energy of the methyl group at the C₍₅₎ atom in molecules of 2,3,5-substituted 1, 3, 2-oxazaborinanes. The resulting value of G⁰ (1 kcal/mole) is half the value of 1, 3, 2-dioxaborinanes and is close to the analogous value in tetrahydro-I, 3-oxazines (1.2 kcal/mole). The differences observed are associated with features of the p--electronic interactions in the heteroatomic fragment of the organoboron ring.