Ethylene glycol: Infrared spectra,AB initio calculations,vibrational analysis and conformations of 5 matrix isolated isotopic modifications

An extension of earlier ab initio calculations is reported which consists in a more detailed structure optimization of conformations investigated earlier, using the previously described as well as a more flexible basis set. The measurement and analysis of infrared spectra of five isotopic modifications, isolated in Ar and Xe matrices, are described. The analysis of the spectra, carried out within the framework of two H-bonded conformations r_e1 and r_e2 predicted by ab initio calculations to be the most stable ones, is complicated by the occurrence of unusually large matrix splittings and irreversible changes of the spectra under irradiation by infrared light. The spectra are interpreted in terms of essentially two slightly different conformers of type r_e1, deformed by the matrix field. The ¹⁸O isotope shifts prove to be important for correct assignment and the least squares fit. A valence force field is given, whose dependence on the conformation of the OH groups and especially on H-bonding is discussed. According to normal coordinate analysis, the effect of the internal H-bond is most pronounced in the COH bend and OH torsion region. The differences of the potential constants of free and bonded OH groups are responsible for a zero point energy differences of about 20 cm^?1 of two isomers of the modification CH₂ODCH₂OH. From experimental evidence for at least a partial equilibration of these two isomers at liquid helium temperature, internal rotation of the OH groups in an Ar matrix may be deduced. Thermodynamic functions of the r_e1 conformation of glycol in the rigid rotor-harmonic oscillator approximation are reported.     

Critical comparison of ICP-OES, XRF and fluorine volatilization-FTIR spectrometry for the reliable determination of the silicon main constituent in ceramic materials

For the optimization of preparation processes for ceramic powders and compacts by pyrolysis of inorganic polymers, the intermediate and final products have to be monitored by in-situ analysis (in its original place) for main, subsidiary and trace components. In the determination of silicon in Si-N-C- based ceramic samples by ICP-OES after pressurized decomposition at temperatures between 220°–250°C too low concentrations of Si were found. Completely independent analytical procedures were applied to trace systematic errors, i.e. XRF after decomposition of the sample in a metaborate/boric acid melt and FTIR-spectrometry after reaction of the sample with fluorine. The low recoveries of Si were found to be due to losses, which amount up to 25% depending on the temperature and time applied for the pressurized decomposition. With the latter two procedures Si can be determined in the %-range with a relative standard deviation of 0.4% and 0.2%, respectively.     

Trigonal-bipyramidale Cluster mit interstitiellen C2-Hanteln in den Chloriden K[M5(C2)]Cl10 (M = La,Ce, Pr) und Rb[M5(C2)]Cl10 (M = Pr,Nd)

Trigonal-Bipyramidal Clusters with Interstitial C₂-Units in the Chlorides K[M₅(C₂)]Cl₁₀ (M = La, Ce, Pr) and Rb[M₅(C₂)]Cl₁₀ (M = Pr, Nd) The chlorides K[M₅(C₂)]Cl₁₀ (M = La, Ce, Pr) and Rb[M₅(C₂)]Cl₁₀ (M = Pr, Nd) are obtained via metallothermic reduction of the trichlorides MCl₃ with potassium and rubidium, respectively, in the presence of metal M and carbon in sealed niobium containers at temperatures between 700 and 900°C. They contain trigonal bipyramids, interstitially stabilized by a C₂ unit, [M₅(C₂)], and crystallize with the hexagonal (K[Pr₅(C₂)]Cl₁₀, Rb[M₅(C₂)]Cl₁₀ with M = Pr, Nd) or monoclinic (K[M₅(C₂)]Cl₁₀ with M = La, Ce) crystal system. The trigonal bipyramids are surrounded by nine inner Cl^? ligands (capping the nine edges) and by 12 (hexagonal) or 13 (monoclinic) outer ligands and are connected via all of the 21 and 22 ligands, respectively. Special features are Cl^a-a-a (hexagonal) and Cl^a-a-a-a (monoclinic) bridges.     

Metalation reactions—XVII : The dimetalation of branched olefins. The question of the aromaticity of the trimethylenemethane dianion and related derivatives

Metalation of methallylbenzenes with BuLi gave dilithio derivatives which were dialkylated with methyl bromide. Derivatives of cross conjugated dianions are obtained preferentially to linear ones. The parent trimethylenemethane dianion² was obtained by metalation of isobutene. Energies and atomic net charges of these and related molecules were calcualted. The question of the aromaticity of these systems is discussed.     

Construction of linearly independent relativistic symmetry orbitals for finite double-point groups including time reversal symmetry

A formalism is developed for the construction of relativistic symmetry-adapted molecular basis functions under consideration of time reversal invariance. The theory is applicable to the finite double point groups C_n, C_nh, S_n, C_nv, D_n, D_nd, D_nh, T, T_h, T_d, O, and O_h. It is based on the LCAO method. A projection operator technique is employed to construct molecular symmetry orbitals from atomic orbitals. The search for linearly independent basis function is simplified by means of group theoretical considerations.     

Hydrogen/liquid vapor radio frequency glow discharge plasma oxidation/hydrolysis of expanded poly(tetrafluoroethylene) (ePTFE) and poly(vinylidene fluoride) (PVDF) surfaces

Modification of fluorine-containing polymers has recently received much attention due to new chemistries allowing for refunctionalization of these materials, especially their surfaces. In this article results are discussed which demonstrate various interesting modifications (including incorporations of ? OH and oxygen comprised functionality) to expanded poly(tetrafluoroethylene) (ePTFE) surfaces. This is effected through the use of low damage, radio frequency glow discharge (RFGD) processes. The low damage conditions, which preserve the original pore structure/morphology of these RFGD treated materials, are supported by Scanning Electron Microscopy (SEM) while the resulting atomic and molecular effects are investigated through other surface analytical methodology. All materials reported in this investigation have been subjected to intensive structural analyses utilizing Electron Spectroscopy for Chemical Analysis (ESCA), Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR–FTIR), and wettability profiles obtained through contact angle measurements using a large series of liquids having varying surface tensions and surface reactive functionality. Through this multitechnique analysis of both expanded PTFE and poly(vinylidene fluoride) (PVDF) treated surfaces, a model is supported which illustrates surfaces possessing both high and low energy regions comprising both oxygen and fluorine functionality in close molecular proximity.     

In Process Citation

The mild oxidation of bactericidal sulphonamides by hydrogen peroxide in acidic medium at room temperature in daylight, is reported. The oxidation products have been isolated by classical chromatography and purified, and their purity has been determined by HPLC. They have been identified by spectroscopy, chiefly by infrared and mass spectroscopy. An oxidation product not previously reported has been isolated and identified. An oxidation mechanism and the kinetics are discussed.