Solid-state high-resolution 29Si NMR in zunyite

High-resolution ²⁹Si NMR spectra of zunyite Si₅Al₁₃O₂₀ (OH,F)₁₈Cl have been studied by magic-angle sample spinning in combination with high-power proton decouplina and polarization transfer. The isotropic ²⁹Si chemical shift depends mainly on the number of Si-O-Si bridges and the bond angles in these bridges connecting the different SiO₄ tetrahedra.     

Zu Herstellung und Konstitution der Verbindung 3 CaO · 3 GeO2 · H2O

On the Preparation and Constitution of the Compound 3 CaO · 3 GeO₂ · H₂O In the temperature range from 100–∽450°C it is possible to prepare under hydrothermal conditions from equimolar mixtures of CaO and GeO₂ the compound 3 CaGeO₃ · H₂O. By n.m.r. measurements of the solid compound it is shown, that there are only OH groups and no molecular water. It seems to be probable that this compound is a trigermanate of the formula Ca₃H₂ [Ge₃O₁₀].     

29Si-MAS-NMR-Untersuchungen an kristallinen Bleisilicaten

Si-M.A.S.-N.M.R. Investigations on Crystalline Lead Silicates The isotropic ²⁹Si-n.m.r. chemical shifts of ten crystalline lead silicates with molar ratio PbO:SiO₂ between 4:1 and 1:1 has been measured. Starting from the known anion constitution the respective ²⁹Si-n.m.r. signals were assigned to silicate structure units (Qⁿ groups). Decreasing ratio PbO:SiO₂ corresponds to significant low-field shifts of the ²⁹Si-n.m.r. signals of definite Qⁿ groups with constant n. This result is of importance to the future investigation of crystalline and vitreous lead silicates with unknown anion constitution.     

Über basische Aluminiumsalze und ihre Lösungen. XI. Vergleichende 27Al-NMR-Untersuchungen am Mineral Zunyit und basischen Aluminium-Salzen mit tridekameren Al-oxo-hydroxo-aquo-Kationen

Basic Aluminium Salts and their Solutions. XI. ²⁷Al-NMR Studies Comparing the Mineral Zunyite and Basic Aluminium Salts of Tridecameric Al-oxo-hydroxo-aquo-Cations Solid-state high resolution ²⁷Al NMR studies of basic aluminum sulphate and the mineral zunyite, both containing tridecameric Al-oxo-hydroxo groups, show different ²⁷Al spectra. While for zunyite both AlO₆ octahedra (0 ppm) and the central AlO₄ tetrahedron (69 ppm) are observed in the spectrum, in the case of the basic aluminum sulphate only the tetrahedrally coordinated Al (59 ppm) is detected by NMR. This behaviour is explained by structural data, which indicate stronger distortions of the AlO₆ octahedra in the case of the basic aluminum sulphate. The increased shielding of the fourcoordinated Al of the basic sulphate is attributed to an increased ionic character of the Al? O bond in this compound.     

Quantenchemische untersuchungen zum mechanismus der elektrophilen substitution. I. Zur potentialhyperfläche des systems benzol/h+

Results of semiempirical calculations (CNDO/2-FK and MINDO/2 methods) for the σ-π complex problem on protonated benzene are given and compared with previous ones. The semiempirical methods were chosen according to the agreement of their results with new theoretical energy data (E_HF + E_korrel) concerning the classical–nonclassical problem of protonated ethylene. By these methods the corresponding part of the energy surface of the benzene/H⁺ system is simulated. The stationary points of this surface are found by a gradient method with complete optimization of the geometry. On the basis of this method we determined the energy profile of a reaction coordinate between the classical (σ-complex) and nonclassical (π-complex) cation. The so called strong π-complex is a saddle point between two σ-complex minima and can be interpreted as transition state of 1,2-proton shifts. Hypotheses for possible minimum energy paths of electrophilic attacks in the given region of the surface are discussed.     

C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis,Spectroscopic Properties,and Quantum‐Chemical Calculations

β,β′‐Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2‐amino‐tetraphenyl‐porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C‐coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C‐linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β′‐coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled‐cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C‐coupled bisporphyrins.