Die Papierchromatographie einfacher Phenole, aromatischer Oxycarbons?uren and aromatischer Oxycarbons?ureamide

Ohne Zusammenfassung     

Sch?dlingsbek?mpfungsmittel

Ohne Zusammenfassung     

Method for measuring chemical diffusion coefficients in solids

Experiments were performed with temperature programmed desorption of hydrogen and deuterium adsorbates on small platinum spheres. Beyond the expected desorption peak of these adsorbates at around 300 K sample temperature an additional desorption peak at higher temperatures was observed. This additional peak is explained by the diffusion of hydrogen or deuterium atoms from the inside of the spheres to their surfaces with final desorption from these surfaces. The visibility of this second high temperature desorption peak is supported by a small diameter of the platinum spheres. Platinum spheres with diameters around 64 μm were used. The sample temperature at which the second peak was observed depends on the parameters: diameter of the platinum spheres, heating rate of the sample and chemical diffusion coefficient of hydrogen or deuterium in platinum. A theory, which assumes that the chemical diffusion coefficient can be described with an Arrhenius ansatz, was developed to simulate the occurrence of the second peak. The combination of these kinds of experiments with the theory gives a method to measure chemical diffusion coefficients. This method can be called temperature programmed diffusion. At 510 K sample temperature the diffusion coefficient 1.61×10⁻¹² m²/s of hydrogen in platinum and the diffusion coefficient 1.40×10⁻¹² m²/s of deuterium in platinum was measured.     

Comparative study of the photochemistry of the azidopyridine 1-oxides

The photochemistry of azidopyridine 1-oxides was studied using an array of glass and matrix isolation techniques. As with room temperature, the photochemistry of 4-azidopyridine 1-oxide is dominated by triplet nitrene chemistry. However, in the case of the 3-azide, matrix photolysis indicates the formation of diazabicyclo[4.1.0]hepta-2,4,6-triene N-oxide and diazacycloheptatetraene N-oxide intermediates as well as triplet nitrene.     

Advantages of organic halogen bonding for halide recognition

The synthesis of a bidentate halogen bonding receptor and a nearly isostructural hydrogen bonding analogue is described. Crystal structures reveal the interactions of each receptor with anions in the solid state, while NMR titrations elucidate bidentate binding and association constants in solution. Of the two, the halogen bonding receptor demonstrates stronger, water resistant halide binding in competitive solvents.     

EPR Studies on Branched High‐Spin Arylnitrenes

The UV (λ>305 nm) photolysis of triazide 3 in 2‐methyl‐tetrahydrofuran glass at 7 K selectively produces triplet mononitrene 4 (g=2.003, D_T=0.92 cm^?1, E_T=0 cm^?1), quintet dinitrene 6 (g=2.003, D_Q=0.204 cm^?1, E_Q=0.035 cm^?1), and septet trinitrene 8 (g=2.003, D_S=?0.0904 cm^?1, E_S=?0.0102 cm^?1). After 45 min of irradiation, the major products are dinitrene 6 and trinitrene 8 in a ratio of ～1:2, respectively. These nitrenes are formed as mixtures of rotational isomers each of which has slightly different magnetic parameters D and E. The best agreement between the line‐shape spectral simulations and the experimental electron paramagnetic resonance (EPR) spectrum is obtained with the line‐broadening parameters Γ(E_Q)=180 MHz for dinitrene 6 and Γ(E_S)=330 MHz for trinitrene 8 . According to these line‐broadening parameters, the variations of the angles Θ in rotational isomers of 6 and 8 are expected to be about ±1 and ±3°, respectively. Theoretical estimations of the magnetic parameters obtained from PBE/DZ(COSMO)//UB3LYP/6‐311+G(d,p) calculations overestimate the E and D values by 1 and 8 %, respectively. Despite the large distances between the nitrene units and the extended π systems, the zero field splitting (zfs) parameters D are found to be close to those in quintet dinitrenes and septet trinitrenes, where the nitrene centers are attached to the same aryl ring. The large D values of branched septet nitrenes are due to strong negative one‐center spin–spin interactions in combination with weak positive two‐center spin–spin interactions, as predicted by theoretical considerations.