A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents. An examination of some catalyst variations for the catalytic reduction of dinitrogen

Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN(3)N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of approximately 65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.     

Stereochemical memory versus Curtin-Hammett behavior in the rearrangement of 1,3-cyclopentanediyl radical cations derived from housanes through structural effects on conformational control

The electron-transfer-catalyzed rearrangement of the housanes 1 affords regioselectively the two cyclopentenes 2 and 3 by 1,2-migration of a group at the methano bridge. Appropriate ring annelation in the intermediary cyclopentane-1,3-diyl radical cation 1(*+) changes the stereochemical course of the rearrangement from complete stereoselectivity (stereochemical memory) for the structurally simple housane 1b to partial loss of stereoselectivity through competing conformational interconversion for the tricyclic housane 1c. Additional cyclohexane annelation, as in the tetracyclic housane 1a, results in complete loss of stereocontrol through Curtin-Hammett behavior, as substantiated by the viscosity dependence on the product ratio of the rearrangement. Whereas in the radical cations 1b(*+) and 1c(*+) the 1,2-shifts (k(2) and k(3)) are faster than the conformational anti <==> syn change (k(1), k(-1)), the reverse applies for the radical cation 1a(*+). Such structural manipulation of conformational effects in radical cation rearrangements has hitherto not been documented.     

Dispersion relation approach to the anomaly in 2 dimensions

We calculate the chiral anomaly in 2 dimensions within a dispersion relation approach and we compare its features with then-dimensional regularization scheme.Supported by Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, Projekt Nr. P8444-TEC     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

Determination of aluminium and chromium in serum by atomic absorption spectrometry

Summary The optimal conditions for the determination of aluminium and chromium in blood serum are proposed. Several sample pretreatment procedures for the purpose are compared. The best results are obtained by sample dilution with nitric acid (0.1 mol/l) and addition of Mg(NO₃)₂ as modifier with a magnesium concentration of 0.2 mg/ml. This procedure has been used for studying the intestinal intake of aluminium by patients after oral administration of aluminium compounds.     

Electroproduction of strangeness

Formalism for the electroproduction of strange particles based on the one photon exchange approximation and the Feynman diagrams representation of hadron current is reviewed. Different photoproduction models are compared with available photo and electroproduction data. New experiments are proposed that may resolve existing uncertainties and inconsistencies. The formation of hypernuclei via kaon electroproduction is investigated theoretically and compared with other reactions involving purely hadronic processes.     

On a class of atmospheres occurring in stellar hydrodynamic theory

Summary A derivation is given of the basic equation governing the behaviour of small disturbances in a stratified compressible atmosphere (with a locally unstable region bounded by semi-infinite stable regions) in which the time of radiative relaxation is constant.By means of a new independent variable that is a function of the equilibrium entropy stratification, various properties of such media can be established in a straightforward manner. A general expression for the wave energy flux is derived, and integral properties arising from this quantity are used to obtain in particular, results pertaining to the eigenfunctions and eigenvalues for strongly radiating systems. In addition, a model of an atmosphere with a strongly-radiating region embedded in a convective zone, and bounded by semi-infinite radiation-free layers is discussed in some detail. The paper is an approach towards providing some preliminary but unified results in the theory of stellar hydrodynamics.

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Résumé Nous donnons une dérivation de l'équation de base qui détermine la propagation des petites perturbations dans une atmosphère compressible stratifiée (présentant une zone d'instabilité locale entre des zones de stabilité semi-infinies) dont le temps de relaxation radiative est constant.Au moyen d'une nouvelle variable indépendante, fonction de la stratification de l'entropie en équilibre, diverses propriétés de tels milieux sont déterminées simplement. On donne une formulation du flux de l'énergie ondulative et on emploie les propriétés intégrales qui en résultent pour obtenir en particulier des résultats concernant les eigenfonctions et les eigenvalues pour des systèmes à forte radiation énergétique. En outre, on étudie en détail le modèle d'une amtosphère caractérisée par une zone à forte radiation insérée dans une zone convective entre des couches semi-infinies sans radiation.Ce travail présente quelques conclusions préliminaires mais cohérentes dans le domaine de la théorie de l'hydrodynamique stellaire.

     

Competition between photodimerization and photocycloaddition of dimethyl 3-dehydrogibberellenate to ethylene, 1,1-dichloroethylene and trichloroethylene

Photocycloadditions of dimethyl 3-dehydrogibberellenate 1 to ethylene, 1,1-dichloroethylene and trich-loro-ethylene were investigated The results exhibited markedly the competition between photodimerization and photocycloaddition of 1, and showed that the yields of cycloaddition products increased with increasing polarity of the olefins. Strangely, photocycloaddition of 1 to olefins was found to proceed through the singlet excited state