Study of the reactione + e −→K + K − in the energy range1350 \leqq \sqrt s \leqq 2400 MeV

Thee ⁺ e ^?→K ⁺ K ^? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ^± form factor |F _F ^±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment.     

Generalization of Dewar's half-electron method for calculating energies of open-shell electronic states

Dewar's “half-electron” model for calculating electronic energies of certain open-shell doublet and triplet states is extended so as to be applicable to the lowest-energy open-shell state of any given symmetry and multiplicity.     

Supramolecular Water Oxidation with Ru–bda‐Based Catalysts

Extremely slow and extremely fast new water oxidation catalysts based on the Ru–bda (bda=2,2′‐bipyridine‐6,6′‐dicarboxylate) systems are reported with turnover frequencies in the range of 1 and 900 cycles s^?1, respectively. Detailed analyses of the main factors involved in the water oxidation reaction have been carried out and are based on a combination of reactivity tests, electrochemical experiments, and DFT calculations. These analyses give a convergent interpretation that generates a solid understanding of the main factors involved in the water oxidation reaction, which in turn allows the design of catalysts with very low energy barriers in all the steps involved in the water oxidation catalytic cycle. We show that for this type of system π‐stacking interactions are the key factors that influence reactivity and by adequately controlling them we can generate exceptionally fast water oxidation catalysts.     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Capturing pressure‐dependence in automated mechanism generation: Reactions through cycloalkyl intermediates

Chemical kinetic mechanisms for gas‐phase processes (including combustion, pyrolysis, partial oxidation, or the atmospheric oxidation of organics) will often contain hundreds of species and thousands of reactions. The size and complexity of such models, and the need to ensure that important pathways are not left out, have inspired the use of computer tools to generate such large chemical mechanisms automatically. But the models produced by existing computerized mechanism generation codes, as well as a great many large mechanisms generated by hand, do not include pressure‐dependence in a general way. This is due to the difficulty of computing the large number of k(T, P) estimates required. Here we present a fast, automated method for computing k(T, P) on‐the‐fly during automated mechanism generation. It uses as its principal inputs the same high‐pressure‐limit rate estimation rules and group‐additivity thermochemistry estimates employed by existing computerized mechanism‐generation codes, and automatically identifies the important chemically activated intermediates and pathways. We demonstrate the usefulness of this approach on a series of pressure‐dependent reactions through cycloalkyl radical intermediates, including systems with over 90 isomers and 200 accessible product channels. We test the accuracy of these computer‐generated k(T, P) estimates against experimental data on the systems H + cyclobutene, H + cyclopentene, H + cyclohexene, C₂H₃ + C₂H₄, and C₃H₅ + C₂H₄, and make predictions for temperatures and pressures where no experimental data are available. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 95–119, 2003     

Non-planar smoulder propagation governed by diffusion

The steady propagation of a thin smouldering front in a half-spacehas been considered. A suitable coordinate transformation hasallowed the region near the leading edge of the front to beexamined for both a maintained planar surface and with surfacecollapse due to material shrinkage. The change in the oxidizerconcentration for a small increment in the propagation speedfor large time and surface collapse has been determined. Theinfluence of two types of nonlinear diffusion on the shape ofthe smouldering front has been found; other cases can be dealtwith in a similar manner.     

Synthesis of 2-iodoglycals, glycals, and 1,1'-disaccharides from 2-Deoxy-2-iodopyranoses under dehydrative glycosylation conditions

Treatment of 2-deoxy-2-iodopyranoses under dehydrative glycosylation conditions afforded pyranose glycals, 2-iodoglycals, and 1,1'-disaccharides instead of the expected glycoside products. While the product distribution revealed that this reaction is very sensitive to the configuration of the 2-deoxy-2-iodopyranose, 2-iodopyranoid glycals can be obtained almost exclusively in good yields by employing 3,4-O-isopropylidene as a cyclic bifunctional protecting group. The behavior of 2-deoxy-2-iodopyranoses during the dehydrative elimination reaction has been analyzed in detail.     

A systematically generated, pressure-dependent mechanism for high-conversion ethane pyrolysis. 1. Pathways to the minor products

The deposition of carbon during hydrocarbon pyrolysis is part of many industrial processes. The rate and nature of deposition depend, in part, on the gas-phase chemistry of the minor pyrolysis products, which serve as deposition precursors. But the specific reaction pathways governing the formation and destruction of these minor gas-phase products are only partially known. We apply an updated version of our automated mechanism generation tool XMG-PDep to the high-conversion, pyrocarbon-depositing ethane pyrolysis system of Glasier and Pacey, to systematically uncover the likely reaction pathways governing the observed minor products acetylene, propylene, 1,3-butadiene, and benzene. Thorough examination by means of sensitivity, equilibrium, and reaction-pathway analyses reveals an extremely complex, intertwined set of reaction pathways controlling these deposition precursors, some of which are not often considered in the wider pyrolysis literature. Large, aggregated sets of disproportionation reactions, for example, appear to play an important role in the formation of benzene. The analyses motivate a companion paper (following paper in this issue) which explores in greater depth the effects of large groups of radical disproportionation reactions, omitted reaction families, and the possibility that pressure changes in the reactor could alter the distribution of the deposition precursors.     

Structure assignment, total synthesis, and antiviral evaluation of cycloviracin B1

The first total synthesis of the antivirally active glycolipid cycloviracin B(1) (1) is described. The approach is based on a two-directional synthesis strategy which constructs the C(2)()-symmetrical macrodiolide core of the target by an efficient template-directed macrodilactonization reaction promoted by 2-chloro-1,3-dimethylimidazolinium chloride 14 as the activating agent. Attachment of the lateral fatty acid chains to the lactide core thus formed features not only one of the most advanced ligand-controlled addition reactions of a functionalized dialkyl zinc reagent to a polyfunctional aldehyde, but also a highly demanding Julia-Kocienski olefination of a tetrazolyl sulfone bearing electrophilic and base-labile beta-hydroxy ester motifs. By virtue of the flexibility of this synthesis plan, it was possible to prepare a series of macrodiolide cores differing only in the absolute stereochemistry at the branching points as well as a host of model compounds for the fatty acid appendices of cycloviracin. Comparison of these derivatives with the natural product allowed us to establish the as yet unknown absolute stereochemistry of 6 chiral centers of 1 as (3R,19S,25R,3'R,17'S,23'R). Thereby, the (13)C NMR shifts of the anomeric position of the beta-glycosides residing at those positions turned out to be excellent probes for the absolute configuration of the attached aglycones. The concise set of data thus obtained also makes clear that the proposed structure of the fattiviracins, a seemingly closely related family of glycoconjugates, is not matched by the published data. Finally, the biological activity of synthetic 1 and some of the key intermediates obtained en route to this natural product was investigated, showing that the entire construct is necessary for appreciable and selective antiviral activity.