Bor11NMR

Bor11NMR, or 11B NMR, is a form of nuclear magnetic resonance spectroscopy that probes the boron-11 nucleus to study boron-containing compounds. The 11B nucleus has a nuclear spin I = 3/2 and natural abundance of about 80%. As a quadrupolar nucleus, its NMR signals are highly sensitive to local symmetry and electric field gradients, which often broaden resonances in solids but can be less pronounced in fast tumbling liquids.

The 11B chemical shift depends strongly on coordination number and ligands. Three-coordinate boron (planar or trigonal) and four-coordinate boron (tetrahedral) appear at different regions of the spectrum, and the exact resonance position is influenced by solvent and substituents. The spectrum is typically referenced to boron trifluoride etherate (BF3·Et2O), set at 0 ppm in many solvents.

Experimental aspects: 11B NMR is less sensitive than 1H NMR, but the high natural abundance of 11B helps. In solution, many boron species yield sharp lines; in solids, lines are broad unless techniques such as magic-angle spinning (MAS) or multiple-quantum MAS (MQMAS) are used. One-bond 11B–1H or 11B–13C couplings can be observed in proton-coupled or heteronuclear experiments.

Applications: 11B NMR is widely used to characterize boron reagents, boranes, boronates, boronic acids, and borate esters, as well as boron-containing polymers and materials. It is a valuable tool for monitoring boron-containing reactions, assessing coordination chemistry, and aiding structural assignments when boron is present.