Homotopie des foncteurs en groupes

Sans résumé     

Halogenures de tellurenyle—iii: Coupure carbone aromatique-tellure par protodetelluration et carbodetelluration intramoleculaire

In the course of electrophilic cyclisation attempts, o-phenyltellurobenzoyl-chloride did not cyclise to telluroxanthone. but isomerised to 2-chloro tellurobenzophenone through intramolecular carbodetelluration. A breaking of the same C_aromatic-Te bond is also realized by protonolysis. This last reaction leads to a preparative method of synthesis of ditellurosalicylic acid, a starting material for synthesis of benzocondensed tellurium heterocycles.     

Evaluating the profitability of advertising for heavily advertised brands: an empirical study

Even companies with large advertising budgets are sceptical of OR models in advertising—such models often appear overly complex, unrealistic and costly to use. Here a simple econometric model is proposed which utilises existing company data. The parameters are estimated for the five leading brands in a sector of the German alcoholic drinks market. Estimates of the short and long run advertising elasticities are made and optimum advertising appropriations are calculated.     

Evidence for an important 13C NMR shielding effect for carbon atoms bearing a heavy chalcogen substituent

An important ¹³C NMR shielding effect on carbons bearing a heavy chalcogen is demonstrated. This effect is parallel to that induced by iodine, but to a lesser extent. For acyclic compounds and for partially saturated heterocycles, there is an excellent linear correlation between the ¹³C chemical shifts of carbons bearing a chalcogen and carbons bearing a halogen atom in the corresponding compound. The linearity of the relationship is less satisfactory with heteroaromatic compounds.     

Horminon,Taxochinon und weitere Royleanone aus 2 abessinischen Plectranthus-Spezies (Labiatae)

Horminone, taxoquinone and other royleanones, obtained from two Abyssinian Plectranthus species (Labiatae). From the coloured glands on the leaves of two botanically unclassified Plectranthus sp. from Abyssinia, a series of royleanones has been isolated, namely royleanone ( 1 ) and 6,7-dehydroroyleanone ( 2 ) from one species, and 6,7-dehydroroyleanone, horminone ( 3 ), taxoquinone ( 4 ), 6β, 7α-dihydroxyroyleanone ( 5 ), 7α-acetoxy-6β-hydroxyroyleanone ( 6 ) and 7-oxoroyleanone ( 7 ) respectively, from the other.     

Synthèse de dérivés imidazopyridiniques et pyridinotriaziniques

Propargylpyridiniums 2-substituted by hydroxylamine or hydrazine moieties cyclize by heating to imidazopyridiniums whereas derivatives substituted by methylhydrazine or N,N' -dimethylhydrazine lead to pyridino-as-triaziniums. These differences are discussed.     

The Crystal and Molecular Structures of Two Acid-Catalysed Rearrangement Products of Taxochinon

The structures of two acid catalysed rearrangement products of taxochinone ( 1 ) have been determined by X-ray analysis. One of the products turned out to be a 20 (10→9) abeo-abietane ( 2 ), the other an optically inactive phenalenone ( 3 ). Crystals of the former compound, C₂₀H₂₆O₃, belong to space group P2₁2₁2₁ with four molecules per cell and the structure was refined with 879 significant reflexions to R = 0.032. Crystals of the latter compound, C₂₀H₂₂O₂, belong to space group P2₁/c with 12 molecules per cell and the structure was refined with 1823 significant reflexions to R = 0.058.     

Solubility of noble metals in hcp metals: A test for the validity of pseudo-potentials

In the calculation of the energy-band structureU _BS dependence of hcp metal-noble metal dilute alloys on the axialc/a and electron per atome/a ratios, we have used two different types of the pseudo-potential for the noble metals in the virtual crystal approximation. By comparing the experimental data on noble metal-simple hcp metal solubility limits with theoretical curves forU _BS, we show how this type of calculation can serve as one of the criteria for determining the solubility limits and the validity of a given pseudo-potential in the dilute alloy limit.     

Selective deoxygenation of sugar polyols to alpha,omega-diols and other oxygen content reduced materials--a new challenge to homogeneous ionic hydrogenation and hydrogenolysis catalysis

An oxygen atom on every carbon--this is the problem! While nature provides linear C(3) to C(6) building blocks in the form of sugar alcohols in large and renewable abundance, they are overfunctionalized for the purpose of most chemical applications. Selective deoxygenation by anthropogenic catalyst systems may be one answer to this challenge.