The phenolic oxidation of a β-methylchalcone

The phenolic oxidation of 2',4-dihydroxy-4'-methoxy-β-methylchalcone using alkaline potassium ferricyanide gives an aurone rather than an isoflavone. This result is discussed in the context of current theories regarding the biosynthesis of flavonoid and isoflavonoid compounds.     

Beitrag zur Analyse von Stibin

Zusammenfassung Es wird ein Verfahren zur Bestimmung von Stibin beschrieben, das sich sowohl zur Analyse von SbH₃ in organischen Lösungsmitteln als auch zur Bestimmung von flüssigem oder festem SbH₃ eignet. Hierbei wird das Stibin mit überschüssigem Brom zu Sb^V oxydiert, danach mit SO₂ zu Sb^III reduziert und dieses oxydimetrisch mit Jod oder Bromat titriert.

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Summary A method is proposed for the determination of stibine, applicable to its solutions in organic solvents and also to the solvent-free liquid or solid substance. The procedure involves oxidation of SbH₃ with an excess of bromine to Sb^V, reduction to Sb^III with SO₂, and oxidimetric titration of the trivalent antimony with iodine or bromate.

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Herrn Professor Dr. C. Mahr zum 65. Geburtstag gewidmet.     

Cover Picture

The cover picture shows a model of the "progenitor-TADDOLs" in front of a panorama of the Fünffingersstocks and the Wenden Glacier in the Titlisgebiet (Switzerland). The model is flanked by a stylized view of the general mechanistic model for the preferred stereochemical pathway of the Ti-TADDOLate-catalyzed reaction of chelating substrates (left) and a blackboard (right) showing formulae of compounds that can be prepared with high enantioselectivity by nucleophilic addition in the presence of titanium TADDOLates. From TADDOL, introduced in 1982, a genuine auxiliary system for the "introduction of chirality" (not only by reaction) has been developed, which, in the final sprint against the competition has a good chance of securing a place on the winning podium. The photograph of the mountain landscape was taken by Dr. J. Frackenpohl, the cover picture was generated by one of the authors (A.H.) of the comprehensive review of TADDOLs in this issue (p. 92 ff.) with the help of the program Povray. Supporting information for this article is available on the WWW under http://www.angewandte.com or from the author.     

Efficient synthesis of sulfonic,phosphoric, and phosphinic esters employing alkylating polymer-bound reagents

The efficient esterification of various sulfonic acids and sulfonates using polymer-bound triazenes based on the triazene T2 linker is described. Esterification of enantiopure alpha-substituted sodium sulfonates was performed in the presence of an alkylating resin without racemization. Racemization is a serious drawback in the esterification route via sulfonyl chlorides because of intermediate sulfene formation. To demonstrate the versatility of this protocol, phosphoric and phosphinic acids have been converted into the corresponding esters as well. All products were obtained in good yield and excellent purities without any further purification steps.     

Pion multiplicity in nuclear collisions

Data on the mean multiplicity of ^- produced in minimum bias proton-proton, proton-neutron and proton-nucleus interactions as well as central nucleus-nucleus collisions at momenta of 1.4–400 GeV/c per nucleon have been compiled and studied. The results for neutron-neutron and nucleon-nucleon interactions were then constructed. The dependence of the mean pion multiplicity in proton-nucleus interactions and central collisions of identical nuclei are studied as a function of the collision energy and the nucleus mass number. The number of produced pions per participant nucleon in central collisions of identical nuclei is found to be independent of the number of participants at a fixed incident momentum per nucleon. The mean multiplicity of negatively charged hadrons per participant nucleon for central nucleus-nucleus collisions is lower by about 0.12 than the corresponding multiplicity for nucleon-nucleon interactions atp _LAB 15 A·GeV/c, whereas the result at 200 A·GeV/c is above the corresponding nucleon-nucleon multiplicity. This may indicate change of the collision dynamics at high energy.     

Codes Based on Complete Graphs

We consider the problem of embedding the even graphical code based on the complete graph onn vertices into a shortening of a Hamming code of length 2^m-1, wherem = h(n) should be as small as possible. As it turns out, this problem is equivalent to the existence problem for optimal codes with minimum distance 5, and optimal embeddings can always be realized as graphical codes based onK _n. As a consequence, we are able to determineh(n) exactly for alln of the form 2 ^k + 1 and to narrow down the possibilities in general to two or three conceivable values.Dedicated to Hanfried Lenz on the occasion of his 80th birthdayThe research for this note was done while the first author was visiting the University of Waterloo and the University of Rome, respectively. He thanks his colleagues there for their hospitality and also acknowledges the financial support of the Consiglio Nazionale delle Ricerche (Italy). The third author acknowledges the support of the National Science and Engineering Research Council of Canada given under grant #0GP0009258.     

A boundedness theorem with application to oscillation of autocatalytic chemical reactions

For a class of dynamical systems of the form , we prove boundedness of all solutions in the positive time direction. We discuss the existence of stable limit cycles for the simplest autocatalytic reaction involving two internal and two external reactants, as well as for a number of other models arising in applications.