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The nuclear magnetic resonances of 51V, g3Nb, lZ1Sb, lZ3Sb, and lS'Ta in solutions of the pentafluorides of these elements were measured. All of these nuclei have large electric quadrupole moments. I n most cases the chemical species observed was identified by spin-multiplet splitting of the metal resonance. In aqueous 48% H F solutions the lBlTa resonance could not be observed; the 12'Sb and lZ3Sb resonances consist of a symmetrical septet, corresponding t o the hexafluoride ion; the g3Nb resonance consists of a single exchange narrowed line; and the 51V resonance co~lsists of a symmetrical quintet, corresponding to the VOF4-ion. In alcohol solution NbF5 disproportionates to form NbF6-, whereas in ether and triethylamine solutions, the complexes NbF5.OEtz and NbF5.NEta are formed. The latter complexes were confirmed by proton resonance measurements. Resonances of 51V in aqueous solutions of V205 and of IU'H4V03 as a function of pH show a parallel behavior and reveal the presence of six different oxyions of vanadium. Five of these resonances are assigned to the species, V043-, VO3-, V 2 0~~-, V3010~-and V02+, on the basis of the resonance line width and the p H range in which the resonance appears.

The solutions were made up by weight and contained 5 mole% solute. At this dil~rtion, sol~rte-solute interactions nlay be ignored. The strongest solution of $-benzoquinone in methylcyclohexane that could be obtained was 1 1nole7~.All the liquids used were of White label or Research grade purity; the p-benzoquinone was purified by repeated sublimation.Chemical shifts were n~easurecl by the side-hand technique using T.M.S. (tetramethylsilane) as internal reference. These are accurate to f 0.1 cycle/sec. Tetra~nethylsilane was chosen because of its sharp resonance over the entire temperature range studied, -100° C to +140° C. RESULTS AND DISCUSSIONThe variation of chemical shift with temperature of dilute solutiolls of acetonitrile, p-benzoquinone, and N,N-diinethylformamide in inethylcyclohexane and toluene are shown in Figs. 1 to 3 respectively. I t is observed that in all three systems the proton S O L V E ? i T : M E T H Y L C Y C L O H E X A N E I o~o -o -o -O -Oshifts are almost completely independent of temperature when methylcyclohexane is used as solvent, confirnming the absence of solute-solvent complex species in these solutions. On the other hand, there is a progressive high-field shift of the solute protoils in toluene solutions as the temperature is reduced.Large shifts to high field occur in the p-benzoquinone-toluene system below +lo0 C. This is the result of the solution becoming more dilute as the solubility of the solid decreases. For this reason, the temperature coefficients of the shifts have been calculated using +lo0 C as the lower limit. The upper limit, +90° C, is fixed by the internal rotational behavior of N,N-dimethylformamide just above this temperature. The temperature coefficients are shown in Table I.The methyl derivatives, toluene and methylcyclohexane, rather than the parent hydrocarbons, were chosen as solvents since their much lower freezing points enable a wide temperature range to be investigated. In addition, certain physical properties, i.e. For personal use only.

Nuclear spin coupling between protons and Hg199 nuclei in CH3HgX and CH3CH2HgX compounds has been investigated. As the X substituent is made more electronegative very large increases in the spin-coupling constant up to 2½-fold were observed. Smaller alterations occur in different solvent media, and alkyl exchange could be observed in several compounds. In the CH3CH2HgX compounds the changes in the spin-coupling constants of the Hg nucleus with the protons in the methylene group and in the methyl group are comparable in magnitude. The results are interpreted in terms of a simplified model for contact interaction employing optical hyperfine structure (hfs) constants. Qualitative arguments are employed to assess the relative importance of other coupling mechanisms. It is concluded that spin coupling arising from electron orbital motion is negligible, and while dipole—dipole contributions may be important, the evidence indicates the Fermi contact interaction is the dominant coupling mechanism.