The Ozonolysis of Haloalkenes in Solution

A review of the ozonolysis of low molecular weight haloalkenes in solution is presented. The reaction products from the fluoroethylene series are discussed in detail. Secondary ozonides can be obtained from these alkenes although the yields decrease markedly with increased fluorination and diminish to negligible quantities with C 2 F 4 . Compared to alkylethylenes, a greater variety of products are obtained including some epoxides and fluorocyclopropanes. Yield data are supplemented by isotopic labeling results to elucidate the ozonolysis mechanism. The evidence indicates that the final ozonides are formed by the three step Criegee reaction mechanism although the stereoselectivity of the reaction differs from nonhaloalkenes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101813/1/198300065_ftp.pd

Räumliche Variabilität und zeitliche Trends des Trockenstressrisikos von Kiefernstandorten in Mecklenburg-Vorpommern

Die Bodenwasserverfügbarkeit bestimmt zu einem hohen Maße die Vitalität von Bäumen und Waldstandorten. In einigen Teilen Euro-pas wurde in den letzten Jahrzehnten eine häufigere Anzahl von Trockenperioden beobachtet, die bereits das Baumwachstum negativ beeinflusst haben. Es wurden langfristige Trends von Bodentrockenheit unter Kiefernstandorten entlang des klimatischen Gradienten in Mecklenburg-Vorpommern mit dem physikalisch basierten Modell LWF-BROOK90 untersucht. Die Ergebnisse zeigen eine zunehmende Anzahl von Trockenstresstagen ostwärts mit abnehmenden Niederschlagssummen. Die klimatischen Unterschiede innerhalb des Landes werden teilweise von den spezifischen Standortbedingungen und Bodeneigenschaften überprägt. Bodentrockenheit hat in den letzten Jahrzehnten deutlich zugenommen, wobei die östlichen Standorte stärker als die westlichen betroffen sind. Die zunehmende Bodentrockenheit konnte auf einen erhöhten Verdunstungsanspruch der Atmosphäre zurückgeführt werden aufgrund höherer Temperaturen in Kombination mit leicht abnehmenden Niederschlägen während der Sommermonate. Um die negativen Auswirkungen künftiger klimatischer Änderungen zu minimieren, sollten Anpassungsmaßnahmen vorzugsweise im Osten des Landes durchgeführt werden

Multiphoton Exchange Processes in Ultraperipheral Relativistic Heavy Ion Collisions

The very strong electromagnetic fields present in ultraperipheral relativistic heavy ion collisions lead to important higher order effects of the electromagnetic interaction. These multiphoton exchange processes are studied using perturbation theory and the sudden or Glauber approximation. In many important cases, the multi-photon amplitudes factorize into independent single-photon amplitudes. These amplitudes have a common impact parameter vector, which induces correlations between the amplitudes. Impact-parameter dependent equivalent-photon spectra for simultaneous excitation are calculated, as well as, impact-parameter dependent gammagamma-luminosities. Excitations, like the multiphonon giant dipole resonances, vector meson production and multiple e+e- pair production can be treated analytically in a bosonic model, analogous to the emission of soft photons in QED.Comment: 28 pages, 7 figures, accepted for publication in Nucl. Phys.

Metal-free syn-dioxygenation of alkenes

Reactions employing inexpensive reagents from sustainable sources and with low toxicity are becoming increasingly desirable from an academic and industrial perspective. A fascinating example of a synthetic transformation that requires development of alternative procedures is the osmium catalysed dihydroxylation. Recently there has been considerable interest in achieving this reaction through metal-free procedures. This review describes the methods available for metal-free syn-dioxygenation of alkenes

Oxidative Cleavage of Alkene C=C Bonds Using a Manganese Catalyzed Oxidation with H2O2 Combined with Periodate Oxidation

A one-pot multi-step method for the oxidative cleavage of alkenes to aldehydes/ketones under ambient conditions is described as an alternative to ozonolysis. The first step is a highly efficient manganese catalyzed epoxidation/cis-dihydroxylation of alkenes. This step is followed by an Fe(III) assisted ring opening of the epoxide (where necessary) to a 1,2-diol. Carbon-carbon bond cleavage is achieved by treatment of the diol with sodium periodate. The conditions used in each step are not only compatible with the subsequent step(s), but also provide for increased conversion compared to the equivalent reactions carried out on the isolated intermediate compounds. The described procedure allows for carbon-carbon bond cleavage in the presence of other alkenes, oxidation sensitive moieties and other functional groups; the mild conditions (r.t.) used in all three steps make this a viable general alternative to ozonolysis and especially for use under flow or continuous batch conditions

Measurement of the Total Cross Section for Hadronic Production by e+e- Annihilation at Energies between 2.6-5 Gev

Using the upgraded Beijing Spectrometer (BESII), we have measured the total cross section for $e^+e^-$ annihilation into hadronic final states at center-of-mass energies of 2.6, 3.2, 3.4, 3.55, 4.6 and 5.0 GeV. Values of $R$, $\sigma(e^+e^-\to {hadrons})/\sigma(e^+e^-\to\mu^+\mu^-)$, are determined.Comment: Submitted to Phys. Rev. Let

Measurements of the Cross Section for e+e- -> hadrons at Center-of-Mass Energies from 2 to 5 GeV

We report values of $R = \sigma(e^+e^-\to {hadrons})/\sigma(e^+e^-\to\mu^+\mu^-)$ for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.Comment: 5 pages, 3 figure

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil