Analysis of the NMR Spectrum of Tetraborane

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Abstract
The 11B NMR spectrum of B4H10 consists of a low‐field triplet exhibiting secondary triplet splitting and a high‐field doublet having extensive fine structure. A reinterpretation of this spectrum is proposed. The triplet structure arises from coupling of 11B in the BH2 groups to the two terminal protons and to the two adjacent bridge protons. The doublet can not be assigned from first‐order considerations. 11B–{1H} double resonance and 10B and 11B substitution studies indicate that the doublet fine structure arises from strong 11B–1H coupling interactions. The signs of JBH and JBBH are shown to be opposite from a comparison of the observed and calculated 11B spectra of tetraborane samples with various 10B/11B isotopic ratios. The proton spectrum of B4H10 consists of a quartet on which is superimposed a broad feature plus several smaller peaks. The spectra calculated for the 11BH2, 10BH2, and BH terminal protons and the bridge protons account for all the peaks in the 1H spectrum. A difference in the ease of rf saturation of the triplet and doublet in the 11B spectrum is attributed to differences in the electric‐field gradients at the BH and BH2 boron sites.

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