Ionen-Cyclotron-Resonanzuntersuchungen an Ionen–Molekül-Komplexen von Anisol und Anisolhomologen

The ion cyclotron resonance spectra of anisol, 3-methylanisol, phenetol, 3-methylphenetol and thioanisol at pressures of 10^?6 Torr resemble the normal mass spectra. Above 10^?5 Torr the spectra show signals due to product ions. As seen from double resonance measurements most product ions are formed by the reaction of a fragment ion with a neutral ether molecule under elimination of alkyl, alkoxy alkylthioradicals or of ethylene. Apart from the molecular ion radical ions do not participate in ion-molecule reactions.     

Cross and ring-closing metathesis of 1,3-diynes: metallotropic [1,3]-shift of ruthenium carbenes

The regio- and stereoselective enyne CM and RCM reactions involving 1,3-diynes have been developed. The ring-closing metathesis of enediynes induces a facile metallotropic [1,3]-shift of alkynyl ruthenium carbene species, thereby providing a unique entry into the synthesis of fully conjugated 1,5-diene-3-ynes.     

Molecular ramsauer-townsend effect in very low energy He-He scattering

It is shown that a Ramsauer-Townsend effect is possible in very low energy (≈ 2°K) collisions of ⁴He-⁴He - i.e., a deep minimum in the total elastic scattering cross section occurs at this collision energy. It is seen that no such minimum is possible for the other isotopic variants, ³He-³He and ³He-⁴He.     

Micro-X-ray fluorescence as a general high-throughput screening method for catalyst discovery and small molecule recognition

A powerful high-throughput screening technique is described for the rapid screening of bead-based libraries for catalyst discovery and molecular recognition. Micro-X-ray fluorescence (MXRF) screens materials for elemental composition with mesoscale analysis. This method is nondestructive and requires minimal sample preparation and no special tags for analysis, and the screening time is dependent on the desired sensitivity. The speed, sensitivity, and simplicity of MXRF as a high-throughput screening technique were applied to screen bead-based libraries of oligopeptides for phosphate hydrolysis catalysts and molecular recognition of selective receptors for the degradation products and analogues of chemical warfare agents. This paper demonstrates the analytical or HTS capability of MXRF for combinatorial screening. It is meant only to show the capabilities of MXRF and is not meant as an exhaustive study of the catalyst and molecular recognition systems presented.     

Synthesis of novel C2-C3'N-linked macrocyclic taxoids by means of highly regioselective Heck macrocyclization

[reaction: see text] Novel C2-C3'N-linked macrocyclic taxoids are synthesized using intramolecular Heck reaction in the key step. Macrocyclization proceeds with high regioselectivity in good yield. Taxoids bearing an olefin moiety at C2 and an iodide at C3'N give exo-products exclusively. However, the endo-products are formed with up to 100% regioselectivity just by switching the positions of the olefin and the iodide moieties. Some of these macrocyclic taxoids are significantly cytotoxic.     

Hydrothermal synthesis and structure of organically templated chain, layered and framework scandium phosphates

Four scandium phosphate-based structures have been prepared hydrothermally in the presence of the primary diamines ethylenediamine and diaminobutane and the primary amine cyclohexylamine and characterised by single crystal and powder X-ray diffraction, ³¹P and ⁴⁵Sc solid-state MAS NMR and chemical analysis. Charge balancing protons in the structures are located using bond valence sum calculations and postulated hydrogen bonding networks. Compound 1, [(H₃NC₂H₄NH₃)₃][Sc₃(OH)₂(PO₄)₂(HPO₄)₃(H₂PO₄)], , a=5.4334(6), b=8.5731(9), , α=79.732(4), β=83.544(4), γ=80.891(5)°, Z=2, is built up of scandium phosphate ribbons, based on trimers of ScO₆ octahedra linked by OH groups. These trimers are joined through phosphate groups bound through three oxygens, and are decorated by phosphate groups linked by a single oxygen atom. The ribbons are arranged parallel to the a-axis and linked one to another by fully protonated ethylenediammonium ions. Compounds 2, [(H₃NC₄H₈NH₃)₃][(Sc(OH₂))₆Sc₂(HPO₄)₁₂(PO₄)₂], , a=13.8724(3), , Z=1, and 3, [(H₃NC₄H₈NH₃)₂(H₃O)][Sc₅F₄(HPO₄)₈], C2/m, a=12.8538(4), b=14.9106(4), , β=101.17(9)°, Z=2, were prepared using diaminobutane as the organic template in the absence and presence, respectively, of fluoride ions in the gel. Compound 2 has a pillared layered structure, in which ScO₆ octahedra are linked by three vertices of hydrogenphosphate groups into sheets and the sheets pillared by ScO₆ octahedra to give a three-dimensionally connected framework isostructural with a previously reported iron(III) hydrogenphosphate. The protonated diaminobutane molecules occupy cavities between the layers. Compound 3 has a layered structure in which isolated ScO₆ octahedra and tetrameric arrangements of ScO₄F₂ octahedra, the latter linked in squares through fluoride ions, are connected by phosphate tetrahedra that share two or three oxygens with scandium atoms. In this structure, the protonated diaminobutane molecules connect the layers, the -NH₃⁺ groups fitting into recesses in the layers. Compound 4, [(C₆H₁₁NH₃)][ScF(HPO₄)(H₂PO₄)], Pbca, a=7.650(3), b=12.867(5), , Z=8, the first scandium phosphate to be prepared with a monoamine, is also a layered solid. In this case, the layers contain single chains of ScO₄F₂ octahedra which share fluoride ions in trans positions. Phosphate tetrahedra bridge across scandiums via two of their four oxygens, both within the same chain and also to neighbouring chains to make up the layer. The protonated amine groups of the cyclohexylamine molecules achieve close contact with phosphates of the layer, while the cyclohexyl moieties, which are in the chair configuration, project into the interlayer space.     

A theoretical analysis of the reaction between hydrogen atoms and isocyanic acid

Using BAC-MP4 potential-surface parameters, supplemented by an MP2 normal-mode analysis at one transition state, and statistical theoretical methods, we have computed thermal rate coefficients for the reactions, and Over the entire temperature range considered, 300 K < T < 3300 K, reaction (2) is the dominant product channel. The theoretical predictions are in excellent agreement with the experimental results available for k₂ and k_?1, the rate coefficient for the reverse of reaction (1). Modified Arrhenius expressions are given for k₁, k_?1, and k₂. In addition, we identify and discuss a weakness in utilizing a Hartree-Fock normal-mode analysis in the prediction of k₂. The present result for k₂ is much smaller than that used in the initial modeling of the RAPRENO_x process. The implications of this are discussed.