B(C6F5)3-Catalyzed E-Selective Isomerization of Alkenes

Herein, we report the B(C₆F₅)₃-catalyzed E-selective isomerization of alkenes. The transition-metal-free method is applicable across a diverse array of readily accessible substrates, giving access to a broad range of synthetically useful products containing versatile stereodefined internal alkenes. The reaction mechanism was investigated by using synthetic and computational methods.     

Water diffusion in atmospherically relevant α-pinene secondary organic material

Secondary organic material (SOM) constitutes a large mass fraction of atmospheric aerosol particles. Understanding its impact on climate and air quality relies on accurate models of interactions with water vapour. Recent research shows that SOM can be highly viscous and can even behave mechanically like a solid, leading to suggestions that particles exist out of equilibrium with water vapour in the atmosphere. In order to quantify any kinetic limitation we need to know water diffusion coefficients for SOM, but this quantity has, until now, only been estimated and has not yet been measured. We have directly measured water diffusion coefficients in the water soluble fraction of α-pinene SOM between 240 and 280 K. Here we show that, although this material can behave mechanically like a solid, at 280 K water diffusion is not kinetically limited on timescales of 1 s for atmospheric-sized particles. However, diffusion slows as temperature decreases. We use our measured data to constrain a Vignes-type parameterisation, which we extend to lower temperatures to show that SOM can take hours to equilibrate with water vapour under very cold conditions. Our modelling for 100 nm particles predicts that under mid- to upper-tropospheric conditions radial inhomogeneities in water content produce a low viscosity surface region and more solid interior, with implications for heterogeneous chemistry and ice nucleation.     

Acuminatanol, the first 2′,2?-bis-dihydrobiflavonol from the aqueous extract of Trichoscypha acuminata

One new 3′,4′,5′,5,7-pentahydroxy-2′,2?-bis-dihydrobiflavonol, acuminatanol (1), was obtained from the aqueous extract of Trichoscypha acuminata. The structure elucidation process was performed primarily utilizing a capillary scale NMR probe. Acuminatanol (1) is the first example of a bis-dihydroflavonol linked exclusively via the B-rings at C-2′ and C-2? positions. To date, it is the first naturally-occurring compound reported from the genus Trichoscypha, and the first new natural product published from our compound libraries generated from the aqueous extracts of American and African plants.     

The identification of synthetic homopolymer end groups and verification of their transformations using MALDI‐TOF mass spectrometry

Recent advances in the resolving power of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) enable the detailed characterization of linear homopolymers, and in particular provide invaluable data for the determination of their end‐group functionalities. With the growing importance of macromolecular coupling reactions in building complex polymer architectures, the ability to accurately monitor end‐group transformations is becoming increasingly important for synthetic polymer chemists. This tutorial demonstrates the application of MALDI‐TOF MS in determining both end‐group functionalities and their transformations for linear homopolymers. Examples of both polycaprolactone and polystyrene are examined, and the strengths and weaknesses of various approaches to data analysis are given. Copyright © 2010 John Wiley & Sons, Ltd.     

Preliminary investigations on novel camphor-derived chiral sulfones: completely stereoselective formation of tricyclic β-hydroxy sulfones from 8- and 10-functionalized camphor derivatives

Some camphor-derived chiral allylic and benzylic sulfones in which the sulfonyl group is located at the C-10, C-9 or C-8 methyl groups of (+)-camphor were synthesized. The C-9 and C-8 substituted sulfones were obtained via Wagner-Meerwein rearrangements of the bicyclic camphor framework. On treatment with LDA, the C-10 and C-8 substituted sulfones cyclized with complete stereoselectivity, affording tricyclic β-hydroxy sulfones whose relative configurations were determined by X-ray crystallography. Tricyclic sulfones 23 and 24 underwent both β-elimination and retro-aldol reactions on further exposure to base. Reduction of the carbonyl group of the C-10 substituted sulfones afforded exo-configured isobornyl sulfones with high stereoselectivity. Reaction of the lithiated isobornyl benzyl sulfone 32 with benzaldehyde generated all four of the possible product diastereomers, of which three were isolated pure by chromatography. Attempted desulfonylation of these diastereomers failed to generate the desired optically active homobenzylic alcohols but the same sulfonyl carbanion trapping/desulfonylation sequence was successful in a model achiral series of compounds.     

Untersuchung von Milch

Ohne Zusammenfassung     

Electron correlations at the fractional quantum Hall edge

This paper reviews tunnel spectroscopy of fractional quantum Hall edges using cleaved-edge overgrown devices. Beginning with an intuitive introduction to various experimental and theoretical aspects, the device structure is reviewed, and the experimental result of a continuum of power-law tunneling exponents is revisited. The unanticipated behavior of the exponent with fractional filling factor is described, and all subsequent theoretical explanations for these results are laid out for comparison. Finally, we propose new directions for experimentally resolving the remaining questions.     

Heterostructures overgrown on GaAs corner substrates

By choosing suitable crystal facets we are able to epitaxially overgrow a precleaved corner-substrate. We are using GaAs (1 1 0)-like facets and growth conditions such that no accumulation or depletion of deposited material near the corner is observed, avoiding morphological changes at the corner during the growth process. So we achieve high-quality layer growth across the corner. With this technique we demonstrate a new type of quantum confinement structure consisting of a GaAs/AlGaAs heterostructure overgrown on top of this precleaved corner-substrate.