Abstract
An experiment involving a moisture-sensitive synthesis and spectroscopic characterization suitable for the advanced inorganic laboratory course is presented. The acid–base complex ammonia borane (AB) is synthesized from the heterogeneous reaction between sodium borohydride and finely ground ammonium sulfate in tetrahydrofuran solvent. AB is isolated as a fluffy white solid. The 1H and 11B NMR spectra of AB, separately measured in the solvents D2O and CD3CN, provide an excellent opportunity to introduce some of the basic concepts of multinuclear NMR spectroscopy. The triplet and quartet peaks observed for the NH3 and BH3 groups in the 1H spectrum measured in CD3CN can be used to discuss the nature of JNH and JBH coupling. The former coupling is rarely observed because the quadrupolar 14N in nonspherical structures experiences rapid relaxation and large J coupling, leading to broad peaks for −NH and −NH2 protons. Although such coupling due to 11B is more commonly observed, a comparison of the 1H NMR spectra...
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