Potential Energy Surface conformer quantum chemistry Conformational Isomerization Dioxaborinane potential energy surface 1,3,2-dioxaborinane Boric Acid Ester Boric Ester Conformational Behavior Cyclic Ester Cyclic Ether ( )- and ( )-isomers 1,3,2-dioxaborinanes 2,5-dimethyl-1,3,2-dioxaborinane 2-methyl-5-nitro-1,3,2-dioxaborinane Alternative Conformer Ammonia Molecule Axial Conformer Boric Acid Boron Atom Boronic Acid Conformational Characteristic Conformational Equilibrium Coordination Bond Dimethyl Ether Ethane Fragment H NMR spectroscopy