The nature of the intermediate formed by the electrophilic addition of H+, F+, Cl+, Br+, +SR, +HgX, or Ag+ to ethylene has been studied by extended Hiickel molecular orbital calculations. The trends observed in these calculations are shown to correlate well with experimental data and chemical intuition. Overlap populations, self-consistent charge distributions, and relative energy differences for these ions are given. Total energy differences for two of the charged species are compared by CNDO/2 calculations. The overall mechanism of electrophilic additions to olefins is discussed in light of these calculations. The relative stability of the intermediates involved in these reactions is determined by the extent of perturbation of the olefin by the attacking electrophile. The mode of addition is influenced by the amount of energy required to convert the symmetrical onium ion II to its unsymmetrical form IV.

who conducted preliminary studies. We are also indebted to Dr.Ikuo Matsubara of the Toyo Rayon Company, Otsu, Shigaken, Japan, for measuring some of the far-infrared spectra.

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The disilicides of Nd-Dy have relatively small c values (0.750 > X S~/ X~I > 0.725), so that the other two axes must increase, which is achieved by the formation of vacancies in one of the Si chains and by increase of the axis dependent on it. The structure of these silicides is therefore orthorhombic and nonstoichiometric.In the digermanides of La-Ce, a large metal and a nonmetal are present (0.750 > R G~/ R N > 0.725). The value of c is large, and, in order to maintain the value for the cell volume, one of the other two axes must de-crease. This is achieved, as can be seen from the orthorhombic structure, by the incomplete filling of one of the nonmetal chains by Ge atoms, so that these digermanides will be orthorhombic.In the digermanides of Pr-Sm the length of c is of an intermediate value (0.760 > Rc~/R,\I > 0.750). The nonmetal chains--depending also on the c axis-are not large enough to accommodate all of the Ge atoms, and vacancies appear in both the a-and b-dependent chains, resulting in nonstoichiometric tetragonal structures.Thermodynamic and spectrochemical data on the donor properties of dimethylcyanamide, ( C H I )~N C S , toward chargetransfer types of acids, conventional Lewis acids, and nickel(I1) are reported. Evidence from changes in the infrared and nmr spectra upon coordination is interpreted to indicate that the nitrile nitrogen is the donor atom. The C'I-H coupling constants are very informative in elucidating the properties of this donor and the structure of these adducts. The donor properties of N,N-dimethylcyanamide are compared with those of acetonitrile and the differences are discussed.