Solutions with pentavalent vanadium contain between pH 3 and 5,5 only decavanadate ions in the forms of H2V1,0zs4-, HV100285-, and V,00286-. The cristallized sodiumas well as the potassium decavanadates containing the ions V,,OZS6-and HVloOzs5-are highly soluble salts. The double salts {K,NaV,oO,,,lOH,O} and {K,NaHV,0028,10H20} on the other hand are so sparingly soluble that they can be used for the quantitative precipitation of sodium. Even from solutions with a ratio K : Na = 10000: 1 the precipitates obtained have an exact stoichiometric composition. 865 Zurich, Laboratorium fur Anorganische Chemie der Eidg. Technischen Hochschule -99. Chemische Verschiebungen in der kernmagnetischen Resonanz von 1 7 0 in organischen Verbindungen1)2) von H. A. Christ3), P. Diehls), HR. Schneider4) und H. Dahn4) (7.111. 61) Von den drei stabilen Sauerstoff-Isotopen besitzt nur I7O ein magnetisches Moment. Da dieses Isotop eine naturliche Haufigkeit von nur 0,037% hat, sind die Kernresonanzlinien ohne kiinstlichen Anreicherung ausserst schwach. Sie konnen nur beobachtet werden, wenn die Probe geniigend Sauerstoff enthalt, d. h. vor allem in kleinen Molekeln, und auch dann nur mit besonders rauscharmen Spektrometern. Daher kommt es, dass trotz der Wichtigkeit von Sauerstoff fur die Chemie bisher wenig uber die 170-Kernresonanz (NMR) in der organischen Chemie bekannt geworden ist. ALDER & Yu 5, wiesen als erste die Kernresonanz von 1 7 0 nach und fanden eine chemische Verschiebung zwischen Wasser und Essigsaure. WEAVER, TOLBERT & LA FORCE^) massen 1955 die chemischen Verschiebungen von 10 organischen und 5 anorganischen Verbindungen ; 1959 erweiterten DHARMATTI, SUNDARA RAO & Vr JAYARAGHAVAN 7) diese Liste urn 10 weitere organische Stoffe. Neuerdings sind ausserdem Arbeiten uber Verschiebungen der Resonanzlinien von Hydratwasser in anorganischen Salzen erschienen *) ; dabei wurde erstmals angereichertes H2'O verwendet .

In carbonyl compounds RCOX (X=H, Me, SiR3, SR, Cl, F, OMe, OH, NH2, O‐; R=H, Me), the 17O shift values of the carbonyl group depend on the electron donor–acceptor properties of X, whereas the 13C shift values are determined by other factors too. By IGLO ab initio calculations, the difference between 13C and 17O has been traced to differences in the relative importance of the shielding tensor component in the direction of the C—O bond (σzz). The deshielding contribution of this component is mainly determined by the energy of the n–π* excitation; donor–acceptor‐type interactions influence the level of both orbitals. As the n orbital of this transition is essentially localized on the O atom, the excitation acts less on 13C and is thus mainly responsible for the difference in substituent sensitivity between 13C and 17O shifts. An analogous difference of substituent sensitivities between 13C and 17O shifts exists in aroyl compounds p‐YC6H4COX towards changes in the para substituent Y; it is explained on the same basis as the effect of X upon RCOX, without the necessity of referring to a ‘reverse’ substituent effect. Finally, the surprising absence of substituent effects upon the 17O shift in aroyl cations p‐YC6H4CO+ can be explained by the fact that, for symmetry reasons, the n–π*‐type excitation is absent in linear compounds. © 1997 by John Wiley & Sons, Ltd.

ChemInform Abstract (the (mostly) p-Y are not given).

The 17O shift values of para‐substituted benzoyl compounds p‐YC6H4COX (X=H, CF3, COOEt, Br, Cl, F, SEt, OCOAr, OH, O‐Na+, NH2) were measured. The 17O shielding values δ(17O) of these and other aryl‐unsubstituted benzoyl compounds (Y=H) follow the electron‐donating power of X (resonance), whereas inductive electron attractors (CF3, COOEt) show only small effects. The sensitivity of the shift values to donor/attractor para substituents Y, measured as the Hammett–Taft ρ+=δ(17O)/σ+, follows both the resonance and the inductive effects; combined with the δ(17O) values, it is proposed as an empirical measure of the polarity (electrophilicity) of the carbonyl group (35 types of COX in Table 1).