Conclusions All modifiactions of the ferric thiocyanate method investigated were affected by atmospheric oxygen. However, the interference in the Hills and Thiel (7) method and the Bolland (3) procedure was not as great as in the Lips, Chapman, and McFarlane (5) method. The results of Lea (8) were confirmed in respect to the lower values obtained when the atmosphere was rigorously excluded. Minimal results by the ferric thiocyanate procedure were possible only when carefully purified nitrogen was employed, and all possible precautions to prevent contact with air were observed. No other satisfactory method for offsetting this interference was found. When the ferric thiocyanate procedures are conducted in the presence of air, the results, while high, are proportional to the iodimetric values. The former method, however, is much more sensitive than iodimetric procedures. Therefore under conditions where only comparative results are desired, such as in the assessment of the activity of antioxidants or in accelerated tests to predict the stability of a fat or oil, the ferric thiocyanate method should prove of considerable value. The Hills and Thiel (7) method was found to be the most satisfactory of those investigated since the use of benzene‐methanol as a solvent permits the use of larger samples and the reagents are considerably more stable than in other methods.

Germanium-73 n.m.r. observations have been extended to a wider range of hydrides, alkyls, and polygermanes, together with further observations on mixed halides. Chemical shifts, coupling constants, linewidths, relaxation times, and derived parameters are reported. The current limits of observa bi lity are indicated As 73Ge is the most difficult Group 4 isotope for n.m.r. work (gyromagnetic ratio, y = -0.9332 x rad T-' s-l, spin I = Q, nuclear electric quadrupole moment, Q = -0.18 x m, natural abundance 7.76%), it is not surprising that there have been only limited reports of its observation. In an earlier paper the enhancement of sensitivity in hydrides and alkyls by proton polarization transfer was explored, and fuller results are now presented.The earliest ',Ge n.m.r. data stem from a survey by Schwenk and co-workers ' which included T2 determinations by the Carr-Purcell sequence. Soon after, Kidd and Spinney observed binary and ternary mixtures of germanium tetrahalides, assigning 73Ge shifts to all possible Cl/Br/I species. More recent work has extended 73Ge observations to germatrane~,,.~ carbofunctional tetra-alkyls,6 shifts and relaxation times of tetrasubstituted germanes 7,8 including methylgermacyclohexanes,9 and to silicon-germanium hydrides." There are few reports on arylgermanes, apart from GePh,, and Ge directly bonded to a transition metal has not been observed. Comparisons of chemical shifts between pairs of C/Si, Si/Sn, and Sn/Pb analogues" have been extendedI2 to include the Si/Ge and Ge/Sn pairs, but with fewer than 30 examples available. Very recently, a fuller study of tetra-alkoxygermanes l 3 produced a different linear relationship between 6(Ge) and 6(Si) for this class of compound, reinforcing earlier 6 , 7 , 1 ' relations based on limited data. We now report further 73Ge observations including chemical shifts, linewidths, coupling constants, relaxation times, and derived parameters. Table 1 lists all the compounds examined by 73Ge resonance in this work. A full listing of all published data, for approximately one hundred compounds, will be published elsewhere.', The only other available data are a handful of coupling constants measured via the bonded element, including 'J(GeH) = -97.6'' or -87.8 Hz l 6 for GeH,, 'J(GeC) = -18.717 and 2J(GeH) = 2.94 Hz'*,19 for GeMe,, 'J(GeF) = 178.5 Hz for GeF," and 98 Hz for CNH4I 2 CGeF,I. ' ' ResultsThe germanium-73 chemical shifts, linewidths, and coupling constants, given in Table 1, were measured on samples ranging in concentration from neat liquids (7-9 mol drn-,), requiring only two or three scans, to about 0.1 mol drn-,, requiring several thousand scans to recognize the signal (signal-to-noise ratio > 2.5). Experimental errors in chemical shifts for clear signals ranged from f 0.1 p.p.m. for sharp signals to & 1 p.p.m. for broad signals, and similarly for the other parameters. The higher polygermanes and methyldigermanes were difficult to free from related species and the results for Ge,H,, Ge4Hl0, and the two dimethyldigermanes are of lower qual...

The acoustic ring signal that dominates NMR spectra of low gyromagnetic ratio nuclei has always been a problem when trying to observe signals from weak samples. This work looks at some ways of improving the observability o f 7 3 G e -one such nucleus.

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