The11B NMR spectrum of B4H10consists of a lowhyphen;field triplet exhibiting secondary triplet splitting and a highhyphen;field doublet having extensive fine structure. A reinterpretation of this spectrum is proposed. The triplet structure arises from coupling of11B in the BH2groups to the two terminal protons and to the two adjacent bridge protons. The doublet can not be assigned from firsthyphen;order considerations.11Bsngbnd;{1H} double resonance and10B and11B substitution studies indicate that the doublet fine structure arises from strong11Bsngbnd;1H coupling interactions. The signs ofJBHandJBBHare shown to be opposite from a comparison of the observed and calculated11B spectra of tetraborane samples with various10B/11B isotopic ratios. The proton spectrum of B4H10consists of a quartet on which is superimposed a broad feature plus several smaller peaks. The spectra calculated for the11BH2,10BH2, and BH terminal protons and the bridge protons account for all the peaks in the1H spectrum. A difference in the ease of rf saturation of the triplet and doublet in the11B spectrum is attributed to differences in the electrichyphen;field gradients at the BH and BH2boron sites.
展开▼
