Two-photon laser spectroscopy of the muonium 1S–2S transition

The 1² S _1/2(F=1)?2² S _1/2(F=1) energy interval in muonium has been investigated by Doppler-free two-photon laser spectroscopy. The transition was observed by uniquely identifying and counting the muons released after the photoionization of the 2S state by the same laser field. The measured transition frequency of 2455 528016(58)(43) MHz is in good agreement with QED calculations. The experiment can be interpreted as a test of the Lamb shift contributions at the 1% level. The method is also well suited for a precise determination of the mass of the positive muon in a muoniumhydrogen isotope shift measurement.     

Systematic computer-aided interpretation of vibrational spectra

The diagnostic value of an interpretation system for vibrational spectra has been investigated in relation to the number of structural units the system can cope with. For five structural units the correlated wavenumber intervals are derived from three infrared and three Raman files by the CRISE program. The interpretative value of each interval in relation to the intensity threshold is discussed. For most intervals a decrease is found on increasing the number of structural units.     

Systematic computer-aided interpretation of infrared and raman vibrational spectra based on the crise program

The CRISE computer program is used to correlate wavenumber regions and 6 structural elements containing carbon, hydrogen and oxygen on the basis of 2 standard files with 549 infrared and Raman spectra. The degree of correlation, including score percentages and interfering percentages, is established for different types of intervals in relation to various intensity thresholds. Specific regions (score 100%, interference 0%) proved to be rare, whereas pseudo-specific regions (score < 100%, interference 0%) are normally present. The usefulness of selective regions (score 100%, interference > 0%) is doubtful. The infrared and Raman results for a structural element can differ appreciably, yet neither technique is clearly superior for interpretative purposes.     

Ruthenium-catalysed carbenoid cyclopropanation reactions with diazo compounds

The transition-metal catalysed cyclopropanation of olefinic bonds using diazo compounds as a carbene source is among the best developed and most useful transformations available to the synthetic organic chemist. Nevertheless, the quest for new catalyst/ligand systems continues in order to further extend the scope of this method and to identify more economical catalytic systems. In this tutorial review, several different ruthenium complexes are presented which have recently emerged as suitable catalysts for carbenoid cyclopropanation. For the model reaction--cyclopropanation of styrene(s) with diazoacetates--and also for some intramolecular cyclopropanation reactions highly remarkable results in terms of catalyst efficiency, product yields, dia- and enantioselectivity have been reported.     

Die Molekül- und Kristallstruktur von Di-μ-sulfato-μ-hydroxo- bis[triamminkobalt(III)]sulfat-8-Hydrat

The crystal structure of Di-μ-sulfato-μ-hydroxo-bis[triamminecobalt(III)] sulfate 8-hydrate has been determined from three-dimensional x-ray data collected by counter techniques. The structure was refined using 2515 independent reflections and the refinement converged to a conventional R factor (on F) of 3.8%. The compound crystallizes in the monoclinic space group C—P2/a, a = 14.122(9), b = 9.858(2), c = 18.81(2) Å, β = 139.3(4), Z = 2, d_obsd = 2.086 g/cm³ and d_calc = 2.14 g/cm³. Within the cation two bidentate SO₄-ligands form bridges between two cobalt atoms. There are two types of S? O bonds (1.50 Å endocyclic, 1.45 Å exocyclic).     

Synthesis of pyrroles from 1-dialkylamino-3-phosphoryl(or phosphanyl)allenes through 1,5-cyclization of conjugated azomethine ylide intermediates

1-Dialkylamino-1,3-diaryl-3-diphenylphosphanylallenes 3a-e are thermally converted into a-annulated 3,5-diarylpyrroles 6a-f and [a]-annulated benzo[c]azepines 7a,b,d. These transformations are likely to include conjugated azomethine ylide intermediates that can undergo either a 1,5- or a 1,7-electrocyclization. The periselectivity is markedly shifted toward 1,5-cyclization when the diphenylphosphanyl substituent is replaced by the diphenylphosphoryl group. Thus, 1-dialkylamino-3-(diphenylphosphoryl)allenes 4a-f yield pyrroles 6 exclusively and with improved yields, unless the 3-aryl substituent in the allene is too electron-rich (e.g., benzodioxol-5-yl, 4f --> 7f). The preparation and thermal transformation of aminoallenes 4 over three or four steps can be conducted as a one-pot procedure, thus providing a convenient synthesis of [a]-annulated 3,5-diarylpyrroles from enaminoketones.     

Template synthesis of a tetraazamacrocyclic ligand with two pendant pyridinyl groups: properties of the isomers of the metal-free ligand and of their first-row transition metal compounds

The one-step reaction of [Cu(en)(2)](2+) (en = 1,2-diaminoethane) with formaldehyde, ethyl 2-pyridyl acetate, and base produces a mixture of [Cu(s-pypymac)](2+) and [Cu(a-pypymac)](2+) (s-pypymac = syn-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane, a-pypymac = anti-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane; syn-to-anti ratio approximately 1:9) in low yield (6%). Ion exchange chromatography is used for isomer separation, and the two isomers of the metal-free ligand are obtained by reduction of the copper(II) complexes and subsequent ion exchange chromatography. Crystal structure analyses of the metal-free a-pypymac ligand, of two isomeric copper(II) compounds of a-pypymac and one of s-pypymac, and of the cobalt(III) complexes of a- and s-pypymac and nickel(II), as well as zinc(II) complexes of a-pypymac, are reported and discussed on the basis of the expectations from force field calculations and from published experimental data of the transition metal compounds of the bis-pendant amine derivative diammac.     

Host-guest antenna materials

The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.     

Stereoisomeric flavor compounds,part LVIII: The use of heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as a chiral stationary phase in flavor analysis

The characteristics of the new chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin are outlined and compared with permethyl- and perethyl-β-cyclodextrins.