. Can. J. Chem. 55,2426Chem. 55, (1977. The exchange of aromatic residues between anilines and anils (transimination) has been shown to be efficiently catalyzed by metal complexes of thiourea. This reaction can be conveniently studied by nmr spin saturation transfer techniques. Experiments of this type using both CW and FT nmr spectrometers are reported. The rate of the reaction is about two orders of magnitude greater than the rates of reactions involving anil formation and hydrolysis with the same substrates and catalysts. The effectiveness of the catalysts vary in the same manner as they do for anil formation and the reaction is similarly subject to inhibition by competing ligands. The rate of exchange of the two inequivalent methyl groups in acetone anils is similarly catalyzed and may be studied by spin saturation transfer experiments. The lifetime of an anil molecule for methyl group exchange is approximately twice that for transimination suggesting that the rate determining process for transimination results in free rotation about the C-N bond so that the methyl groups have an equal probability of retaining or exchanging their environments. [Traduit par le journal]

Publication costs assisted by the National Research Council of CanadaAnisotropic EPR spectra detected at 30 K in y-irradiated powdered BaGeF6, KzSnF6, and BaPbF, have been assigned to the hexafluoride anion radicals GeFl-, SnFl-, and PbFl-, respectively. These species are members of a series of paramagnetic hexafluorides of the elements of groups 4-7 which constitutes one of the largest known groups of isoelectronic free radicals. The nature of the semioccupied orbital in this type of radical is discussed in the light of unpaired electron spin densities computed from the measured hyperfine interactions for the hexafluorides.

The ESR spectra of ClFg, BrFg, and IFg in solid SFg have been reexamined. The observation of formally forbidden or "NMR" transitions for the latter two radicals has permitted the precise determination of their ESR parameters, hitherto known only approximately. Analysis of anisotropic spectra observed at 27 K clearly shows that the halogen hexafluorides possess Ofl symmetry. In these radicals the unpaired electron occupies an antibonding aJg orbital consisting primarily of central-atom ns and fluorine 2p" atomic orbitals. Temperature dependences noted for the line widths and hyperfine interactions are indicative of the presence of a very low-frequency deformation mode in these molecules. The results of INDO calculations for ClFg are in essential agreement with the experimental findings.

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