No abstract

No abstract

No abstract

No abstract

No abstract

The a,w-dihaloalcanes could serve as model compounds for polyethylenes in further studies of infrared and Raman-spectra. The 1,12-dibromododeca1~, belonging to this class of compounds, has the monoclinic space group P 2Ja with the cell parameters a = 24.8 A, b = 5.40 A, c = 6.50A, = 9 9 O , 2 = 2. The preparation of crystals was very difficult. The crystal finally used gives only few and bad X-ray data measured by film method (equiinclination Weissenberg). Therefore the accuracy of the structure determination is not high, but the result is reliable and has model character for related compounds.All molecules are ordered with their long molecular axes parallel to the (401) planes of the unit cell. There are alternating plane layers of bromine atoms on the one hand and aliphatic parts of the molecules on the other hand, both parallel to the (100)-planes. This molecular arrangement explains well the spectroscopic and crystal optical properties of the structure and also of related compounds like 1,lO-dibromodecane and 1,18-dibromooctadecane.

No abstract

The isomerization of meta-xylene under normal pressure was studied in the temperature range 570-770 K on three catalyst series, oiz. (i) gallosilicates with a constant Si/Ga ratio of 50, but different synthesis times ranging from 5 to 96 h, (ii) gallosilicates with a higher (100) and lower (25) Si/Ga ratio after 48 h and 96 h crystallization time, and (iii) a series that included a ZSM-5 zeolite, a gallosilicate, and a ferrisilicate, all with comparable concentrations of Brernsted acid sites. The characterization of the catalysts is based on XRD, electron microscopy (TEM, SEM), ammonia thermodesorption, thermoanalysis and n-hexane adsorption. Synthesis products that were characterized by X-ray diffraction to have 100% crystallinity, aquire further acidity when the synthesis time is prolonged. This effect is due to an additional insertion of galtium in framework positions from a reservoir of nonfrarnework gallium species. -The isomerization on gallosilicates proceeds with negligible disproportionation to toluene. The activity is intermediate, compared to the ZSM-5 zeolite and to the ferrisilicate. The shape selectivity of the gallosilicates is inversely related to the crystallinity. -The kinetics of the isomerization can be described by a parallel two step model, in good agreement with experimental results. The significance of internal mass transport effects is discussed.Sample C2 is identical with sample A6. Sample B3 is identical with sample A6.' ' Sample B4 is identical with sample A7. Ber. Bunsetiyes. Phys. Chem. 96 ( I 992) No. 4 Ber. Burisunyr.~. Phys. Chnri. 96 / 1992) No. 4 I'CH Vr~ltrys~/esr//schrI/i mhH, W-6940 Weiriheim. lYY2 0005-902ljU2J0404-O~Y7 $ 3.50-k .25jO