Unusually large discrepancies exist between the reported values of the experimental geometries of hexafluorocyclobutene determined from microwave (MW) spectroscopy and those from electron diffraction (ED). In an attempt to explain the origin of the difference, the geometries of cyclobutene, 1,2-difluorocyclobutene, 3,3,4,4-tetrafluorocyclobutene, hexafluorocyclobutene and 1,2-dichloro-3,3,4,4-tetrafluorocyclobutene are optimized by ab initio calculations at the Hartree-Fock, second-order Møller-Plesset perturbation levels of theory and configuration interaction with single and double substitutions. Comparison of the calculated results with available MW and ED parameters imply that MW geometrical parameters are probably more accurate for hexafluorocyclobutene than ED ones. The difficulty associated with vibrational corrections for hexafluorocyclobutene appears to be responsible for the unusual pattern of the difference between MW and ED structures.

A series of catalysts, NiO—ZrO2/SO42−, for ethylene dimerization were prepared by coprecipitation from a solution of a nickel chloride-zirconium oxychloride mixture followed by modifying with H2SO4. On the basis of the results obtained from X-ray diffraction and differential thermal analysis, the addition of nickel oxide to ZrO2 or modification with H2SO4 shifted the transition of ZrO2 from amorphous to a tetragonal phase at higher temperatures due to the interaction between nickel oxide (or sulfate ion) and ZrO2. Infrared spectra of the catalyst modified with H2SO4 showed bidentate sulfate ion coordinated to Zr4+ or Ni2+. NiO—ZrO2 without sulfate ion was inactive for the ethylene dimerization, but NiO—ZrO2/SO42− was found to be very active even at room temperature. The high catalytic activity of NiO—ZrO2/SO42− was closely correlated with the increase of acid strength by the inductive effect of sulfate ion. The decrease of catalytic activity above 450°C of evacuation temperature was due to the structural change from amorphous phase to crystalline and the sintering followed by the decrease of surface area.

The adsorption properties of CO on the cation exchanged natural zeolite, and cation effects upon the CO adsorption were studied. exhibited relatively good CO adsorption capacities and treated by 0.4 N- solution proved itself as the best adsorbent and superior to the synthetic zeolite 4A and 5A. The observed adsorption tendency due to the cations were in the order of $Ba^{2+}>Cu^{2+}>Na^+>K^+>Mg^{2+}>Ca^{2+}$. The cation exchanged number per unit cell as well as the kind of cation which forms bond with CO molecules in different intensities and other mineral factors such as pore size indicated to be important factors to the CO adsorption properties. The CNDO/2 calculations were performed to compare the adsorption tendencies and CO interaction energy of cations in .

CNDO/2 calculation for atomic charges, Wiberg bond orders and adsorption energies of CO molecules on the cluster model whose Si/Al ratio varied were carried out.

Infrared absorption spectra of alkyl alcohols in the OH stretching region were obtained from varying the concentrations of alcohols in . The OH stretching bands were broadened and shifted to lower frequencies due to the hydrogen-bond formation. Three bands were obtained from the breakdown of these bands by the simplex method. Each band was assigned to various types of hydrogen-bonded OH groups. The electronic structures and interaction energies of dimeric and trimeric alcohols were calculated by semi-empirical MO(CNDO/2, INDO) methods. These results were in good agreement with those of deconvoluted ir spectra. The EDA(electron donor-acceptor) effect of alkyl group on hydrogen-bond formation was in the decreasing order of butyl > propyl > ethyl > methyl group. On the other hand, the experimental results were in the order : propyl > ethyl > butyl > methyl group. This seemed to be ascribed to the bulkiness of butyl alcohol.

The CNDO/2 method has been used to calculate the electronic structure of the zeolites and silicas, and to investigate the interaction of CO molecules with the OH groups or the exchanged cation in the zeolites. The interaction energies of CO molecules with OH groups in silica were ca. 12kcal/mol, the bond distance, R(O-HC) was 2.6. The strength of bond between CO molecules and various types of cations in the zeolites was in the following order: $H^+ Li^+ > Na^+$. And these energies depended on the amount of charge density transfered from the skeleton to the cations in order to compensate its negative charge.

NiO-ZrO2/SO 4 -2 catalysts were prepared by coprecipitation from the solution of nickel chloride -zirconium oxychloride mixture followed by treating with H2SO4 NiO-ZrO2 alone without SO 4 -2 was inactive as a catalyst for ethylene dimerization, but NiO-ZrO2/SO 4 -2 was found to be very active even at room temperature. The high catalytic activity of NiO-ZrO2/SO 4 -2 was closely correlated with the increase of acid strength by the inductive effect of sulfate ion adsorbed on NiO-ZrO2. The decrease of catalytic activity above 150‡C of evacuation temperature was explained in terms of the structural change of catalyst from amorphous phase to crystalline, and the sintering.

was modified by treating with and by treating witb followed by oxidation. The oxidized species and oxidation state of sulfur compounds were investigated by infrared and X-ray photoelectron spectroscopies. The generation of strong acidity of modified was independent of the sulfur source after oxidation. The sulfur () in the highest oxidation state was responsible for the superacidic property of the modified .

Obtention d'un catalyseur mixte NiO-ZrO 2 , modifie par des ions SO 4 2− , PO 4 3− ou BO 3 3−