Chemical shifts organogermanium compounds

See introductory remarks in Section I.A.4. Information on NMR spectra of organogermanium compounds appears in Table 2. Most sources usually include chemical shift values, S, and coupling constants, J, however, in many cases other features are also discussed. A general discussion of 73Ge NMR appeared in the literature57. 

Recent advances in Ge NMR spectroscopy are reviewed. Following the introduction (Section 1), Section 2 describes recently determined chemical shifts and linewidths for a variety of organogermanium compounds which range from normal (tetravalent) to hypercoordinated (up to heptavalent) species. The role of linewidth as evidence for hypercoordination is discussed. In Section 3, coupling constants, relaxation times and relaxation mechanisms are discussed in detail, showing that in some cases a mechanism other than quadrupolar is involved. In the last section, high-resolution solid-state Ge NMR spectroscopy is covered which has not been treated in previous reviews. 

Although compounds 89-93 exhibit a substantial low frequency shift as compared with 66, compound 95 shows much the same low frequency shift. Hence, this shift should be due to a -7-011601 rather than to hypercoordination. It is interesting to note, however, that there is a rough linear relation l oe = 0.025 5si — 0.049 R = 0.972)) between the Ge chemical shifts of 89, 92, 93, 66 and Si chemical shifts of related silanes. Such linear relations have long been known to exist between related organogermanium and organosiUcon compounds... 

Hypercoordination of silicon in organosihcon compounds has often been associated with a considerable low frequency shift of Si signals. It is expected that the same effect will be observed for the Ge NMR spectra of hypercoordinated organogermanium compounds. The Ge NMR spectra of tris(o-substituted phenyl)germanes were examined and it was found that the Ge chemical shifts (summarized in Table 11) are not necessarily correlated with hypercoordination. 

High resolution solid-state MAS Ge NMR spectra of organogermanium compounds have been observed for the first time the chemical shifts and linewidths of tetraphenylgermane (38) and tetrabenzylgermane (137) were recorded with and without high-power decoupling. ... 

The Ge NMR chemical shifts of several methyl-and phenyl-substituted germacyclohexanes have been determined, and it has been shown that the chemical shifts are very sensitive to steric effects and can provide a useful tool for the conformational analysis of organogermanium compounds. 

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