Hochauflösende Festkörper-NMR-Untersuchungen an Kieselsäuren. III Hochauflösende 29 Si-Festkörper-NMR-Untersuchungen an synthetischen siliciumreichen Kieselsäurehydraten

Solid-State High-Resolution N.M.R. Studies of Silicic Acids. III. Solid-State High-Resolution ²⁹Si-N.M.R. Studies of Synthetic Highly Siliceous Silicic Acid Hydrates Solid-state high-resolution ²⁹Si-N.M.R. experiments were used to study the structure of the silicate layers in three synthetic highly siliceous silicic acid hydrates obtained by cation exchange reactions from the synthetic sodium silicate hydrates ilerite, magadiite and kenyaite. For each of the studied samples two well-separated N.M.R. signals have been recorded which could be assigned to Q³ - (O?Si(OSi?)₃–) and Q⁴-(?Si(OSi?)₄–) units of the silicate layers of the corresponding silicic acid hydrate. On the basis of these results the same model was used to describe the structure of the silicate layers in the studied compounds which has been already used for the interpretation of the N.M.R. results in case of the synthetic sodium silicate hydrates. Compared with the sodium silicate hydrates in the studied silicic acid hydrates a somewhat large Q⁴/Q³-ratio and a high-field shifted Q³signal have been detected. These observations were attributed to structural changes which appeared as a result of the cation exchange reactions.     

Relative Raman Intensities in C<Subscript>6</Subscript>H<Subscript>6</Subscript>, C<Subscript>6</Subscript>D<Subscript>6</Subscript>, and C<Subscript>6</Subscript>F<Subscript>6</Subscript>: A Comparison of Different Computational Methods

The accuracy of various computational methods (Hartree–Fock, MP2, CCSD, CAS-SCF, and several types of DFT) for predicting relative intensities in Raman spectra for C₆H₆, C₆D₆, and C₆F₆ was compared. The predicted relative intensities for ν₁ and ν₂ were compared with relative intensities measured by an FT-Raman spectrometer. While none of these methods excelled at this prediction, Hartree–Fock with a large basis set was most successful for C₆H₆ and C₆D₆, while PW91PW91 was the most successful for C₆F₆.     

Vom Rohöl zu Energie‐ und Chemierohstoffen. Erdölverarbeitung in der Mineralölraffinerie

Crude oil still is one of the most important sources of primary energy. With an annual consumption of nearly four billion metric tons it is also the most important raw material for the chemical industry. The complex process network of a modern oil refinery is used to upgrade crude oil into a wide variety of intermediates and products.     

Isomorphism in the KTaWO<Subscript>6</Subscript>-RbTaWO<Subscript>6</Subscript>-CsTaWO<Subscript>6</Subscript> system

Synthetic procedures have been developed and compounds of composition K _x Rb _y Cs _z TaWO₆ (x + y + z = 1) have been obtained. Their structure has been investigated by X-ray diffractometry. It has been shown that a continuous series of solid solutions is formed in the ternary system under study. Thermal decomposition of A^ITaWO₆ compounds (A^I = K, Rb, Cs) has been investigated by high-temperature X-ray diffractometry.