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The complex formation of TBP in the systems-TBP-water, TBP-nitric acid, and TBP-uranyl nitrate was confirmed by means of infrared spectroscopy. The infrared spectra of uranyl nitrate in the system TBP-nitric acid-uranyl nitrate lead to the conclusion that the competition extraction of both uranyl nitrate and nitric acid takes place during the extraction process.

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Self-association of dipolar substances is studied by 13C magnetic resonance. The dilution shifts in carbon tetrachloride are analyzed in terms of the monomer–dimer equilibrium. Downfield 13C shifts of the nitrile and carbonyl groups are observed for the formation of the dimer of acetone, acetonitrile, and ethyl acetate. Upfield 13C shifts, on the other hand, are observed in the methyl and methylene groups of acetone, methylethyl ketone, ethyl acetate, acetonitrile, propionitrile, nitromethane, nitroethane, N,N-di-methylformamide, and N,N-dimethylacetamide. The equilibrium constants are 0.1–0.5 in units of mole fraction. The downfield 13C shifts of the nitrile and carbonyl groups are interpreted in terms of electric (reaction) field effects imposed by another molecule through dimer formation. The alternation of polarity by polarization of the X–Y group explains the upfield 13C shifts of methyl and methylene groups as shown in the following scheme: Hs+—C−—X+—Y−, where X—Y stands for C=O, C≡N, and NO2 groups which have been classified as –I− groups by Pople and Gordon.

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