Theoretical study of the mechanism of nucleophilic substitution in cyclobutane derivatives

The mechanism of nucleophilic substitution in cyclobutane derivatives has been studied by means of ab initio molecular orbital computations on a model system. The results are in favour of a reaction which proceeds with inversion of configuration, in agreement with experimental data.     

Geometry of acetylene chemisorption on Ni(100) investigated by leed intensity analysis: The c(2 × 2) structure

Results from LEED dynamical calculations performed on the Ni(100) c(2 × 2)C₂H₂ structure, produced by adsorption of C₂H₂ at about 273 K and 1.5 L exposure, are reported. Among the several model geometries tried, the most favoured one appears to be a distorted acetylene molecule with the midpoint of the CC bond (1.20 Å long) placed above the fourfold hollow site at a vertical distance 2.02 Å from the topmost Ni layer and with the CC axis itself tilted by 50° with respect to the surface normal in the [011] direction. In this geometry the NiC distance is 2.2 Å.     

Insertion of the Pt(PPh3)2 unit into inorganic triatomic rings coordinated to metal—ligand moieties

Reaction of the [(triphos)Co(E₂S)]BF₄ complexes (triphos = 1,1,1-tris(di-phenylphosphinomethyl)ethane, E = P or As) containing the P₂S or As₂S cyclic units trihapto(η³-bonded to the metal, with (C₂H₄)Pt(PPh₃)₂ involves insertion of the Pt(PPh₃)₂ moiety into a bond of the inorganic ring, yielding the compounds [(triphos)Co(E₂S)Pt(PPh₃)₂]BPh₄ (E = P or As), whose structures have been determined by X-ray diffraction studies.     

Ab initio valence bond calculations. I. Methylene

An ab initio valence bond (VB ) method for calculating energies and wave functions for simple electronic systems is described and the results of its application to methylene are given together with extensive comparisons with previous theoretical results.     

Determination of ultra-trace levels of gold in size-segregated atmospheric particulate samples by laser induced fluorescence: towards an aerosol tracer

A method is described for measuring the gold content of integral and size-segregated samples of atmospheric particulate matter. After acid digestion and a liquid/ liquid extraction, the sample are analysed by Two-Colour Laser Induced Fluorescence in a graphite furnace. An absolute instrumental detection limit of 1 fg is achieved. Assuming a sampled volume of 1 m³, this corresponds to an atmospheric concentration of 50 fg m^–3. Due to blank limited noise, the above limits increase to 20 fg and 1 pg m^–3, respectively. Results of the analysis of filter samples as well as of size-segregated impactor samples are presented.