Hochfeld-27Al-NMR-Untersuchungen zur Aluminiumkoordination in kristallinen Aluminiumphosphaten

High-field ²⁷Al-NMR Investigations on the Aluminium Coordination in Crystalline Aluminium Phosphates The ²⁷Al NMR spectra of crystalline aluminium phosphates obtained at high-magnetic fields under magic-angle spinning (MAS) conditions allow a direct determination of the aluminium coordination. So for five new Al phosphates it is shown that, as it is almost exclusively the case for Al phosphates of known structures, the Al is octahedrally coordinated, too. Chemical shifts between ?13 and ?21 ppm for isolated AlO₆ octahedra, and 39 ppm for isolated AlO₄ tetrahedra (in crystalline AlPO₄), were determined. In comparison to the results on aluminates and aluminum oxides these values are generally upfield-shifted about 30 ppm. The stronger magnetic shielding is attributed to the influence of the phosphorus atoms present in the second coordination sphere of the aluminum.     

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.     

Strukturuntersuchung an biradikalen vom typ des schlenk'schen und des tschitschibabin'schen kohlenwasserstoffs

Die Synthese von Schlenk'schen und Tschitschibabin'schen Kohlenwasserstoffanaloga mit unterschiedlich verbru¨ckten Dibiphenylmethyl-Ha¨lften wird beschrieben. Mit Hilfe von EPR-Pulverspektren lassen sich bei den regellos orientierten Zweispinsystemen intramolekulare Elektronen-Spin-Spin-Kopplungen zu Triplettzusta¨nden erkennen. Aus der Gro¨sse der Nullfeldaufspaltung wird zuna¨chst anhand einfacher Moleku¨lmodellbetrachtungen auf die Moleku¨lkonformation geschlossen. Insbesondere werden jedoch mit Hilfe quantenmechanischer Modellrechnungen und durch Vergleich der Rechenergebnisse mit den experimentellen Daten detailliertere Strukturuntersuchungen durchgefu¨hrt. Dabei wird der Einfluss der Verdrillung zwischen den einzelnen Phenylringen und damit auch der cis- oder trans-Orientierung der ha¨lftigen Spindichtezentren auf die Gro¨sse der D-Parameter ermittelt. Eine Klassifizierung der einzelnen Zweispinsysteme nach ihren magnetischen Eigenschaften wird diskutiert.     

On an inconsistency connected with koopman's theorem

On the basis of Koopmans' theorem two methodically different ways to estimate the effect of a spin-orbit perturbation on the ionization potentials of I₂ have been proposed. In the present paper a model system is constructed to show the equivalence of both methods.     

Sensitized schiff's reagent as an acid-base indicator

The sensitized Schiff's reagent has been used as an indicator in the neutralization of strong acids by means of strong or weak bases. (1) Since the acid to alkali transition is much sharper than the reverse process, the titration is best done by adding alkali to the acid. (2) The results are compared with those of titrations using methyl orange as indicator. (3) The end-point is very sharp with sensitized Schiff's reagent, the transition taking place from a dull red colour to an abrupt rise in intensity. (4) Acids which are comparable in strengths or weaker than H₂SO₃ cannot be titrated with this reagent as indicator.     

Vinylogous dieckmann condensation: an application of Baldwin's rules.

Vinylogous Dieckmann condensations equivalent to enolexo-exo-trig and enolendo-exo-trig cyclisations have been investigated. Five membered rings were smoothly obtained from the former whereas the latter cyclisations occurred with six but not with five membered ring systems.     

Quantitative temperature mapping within an operating catalyst by spatially resolved 27Al NMR

Spatially resolved NMR is employed to quantitatively map the temperature of a solid catalyst under operating conditions during H(2) oxidation with O(2) over Pt/γ-Al(2)O(3). As this new non-invasive in situ technique utilizes the (27)Al NMR signal of the solid phase, it is suitable for catalyst temperature mapping in both liquid- and gas-phase heterogeneous catalytic processes.     

2'-Desoxytubercidin: synthese des o-3'-phosphoramidites und kondensation zu 2'-desoxytubercidylyl(3' → 5')-2'-desoxytubercidin

The phosphoramidite of 2'-deoxytubercidin (2) has been prepared by phosphitylation of compound 3b with chlorodiisopropylaminomethoxyphosphane. The intermediate 3b was obtained from 2'-deoxytubercidin (1) by N⁴-benzoylation and subsequent O-5'-dimethoxytritylation. Condensation of compound 2 with O-3'-silylated 3e gave the fully protected dimer 4b, which was converted into 2'-deoxytubercidylyl (3' → 5')-2'-deoxytubercidin(4a). Compound 4a isoster with 2'-deoxyadenosylyl(3' → 5')-2'-deoxyadenosine (d(ApA)) exhibits a hypochromicity of 11% (270 nm) due to strong stacking interactions. Cleavage of the dinucleoside monophosphate 4a with nuclease S₁ occurs five times faster than that of d(ApA). This shows that the single strand specific enzyme recognises the geometry of the stacked nucleobases.     

5'-Substituted 2,2'-anhydrouridines

3',5'-Di-O-acetyl-2'-halogenouridines (1a, 1c and 1d) can be partially deacetylated at C-5' by transesterification with methanol-HCl, providing the 3'-O-acetyl derivatives 2a–2c. These can be converted into the 5'-O-mesyl derivatives 3a–3c, and latter into the 5'-chloro compounds 3d-3f. All 5'-substituted 2'-halogeno compounds give the corresponding 2,2'-anhydrouridine derivatives 4a–4c on treatment with NaOMe. Structures were proved by IR and ¹H-NMR.     

Dosage de l'hydrogene,de l'azote et de l'oxygene dans le monocarbure d'uranium

A method is described for the determination of hydrogen, oxygen and nitrogen in uranium monocarbide. Hydrogen and oxygen are determined by the classical or modified “Platinum flux” method at 2000° with a coefficient of variation of 10%. Nitrogen is determined at 2000° by the modification of the “Platinum flux” technique. The results obtained are in agreement with those found by Kjeldahl analysis. The coefficient of variation is about 10%. A procedure for the simultaneous determination of the 3 gases is given.     

Couplage selectif d'azaallyllithium et d'arylallenes : synthese generale d'arylmethylenepyrrolidines

1–3 Cycloaddition of 1,3-diphenyl-2-azallyllithium with arylallenes affords a general synthetic method for arylmethylenepyrrolidines, a new class of five-membered-heterocycles.     

Selective kinetic determination of pyridoxal-5'-phosphate with an ammonia gas-sensing electrode

The coenzyme pyridoxal-5'-phosphate (PLP) is deiermined by in situ measurement of the rate of ammonia production using a potentiometric gas-sensing membrane electrode. It is shown that the initial rate of ammonia liberation from L-tryptophan by action of tryptophanase apoenzyme and the coenzyme can be linearly related to PLP levels in the nanogram range with minimal interference from related compounds. Calibration data for the 1 × 10^-7–2.5 × 10^-6 M range for PLP yielded a least-squares equation of rate (mV min^-1) = (0.64 ± 0.01) C — 0.01 ± 0.02 with a standard error of 0.02 mV min^-1, where concentration, C, is expressed in units of 10^-7 mol l^-1.     

Synthesis of licoflavone-a and 6',6'-dimethylpyrano(2',3':7,8)flavone

Licoflavone-A assigned structure of 6-C-prenyl-7,4'-dihydroxyflavone 5 has been synthesized by condensing 5-C-prenyl-2-hydroxy-4-prenyloxyacetophenone 2 with p-prenyloxybenzaldehyde in the presence of alkali. The resulting chalcone 3 on cyclodehydrogenation with DDQ gave 6-C-prenyl-7,4'-diprenyloxyflavone 4 which on boiling with aqueous morpholine afforded the natural product. This synthesis uses, for the first time, protection of phenolic hydroxyls by O-prenylation and DDQ for conversion of chalcone to flavone. 6',6'-Dimethylpyrano (2',3':7,8)navone 8 has been synthesized by the Hlubucek reaction of 7-hydroxyflavone 6 with 2-chloro-2-methyl-3-butyne.     

M/'ethode d'analyse qualitative des cations sans s/'eparations syst/'ematiques

The authors have formerly described a qualitative method for the analysis of Cations according to which separations were reduced to a minimum, each metal being detected by an independent test.They presently seek to improve this method, with special regard to the case when small quantities of an element are to be found in the presence of large proportions of one or more other cations.In this first paper are given the results for the following metals arsenic, tin, antimony, bismuth.