Direct determination of absolute configuration of methyl-substituted phenyloxiranes: combined experimental and theoretical approach

Three possible methyl-substituted phenyloxiranes have been synthesized in enantioenriched form (89-99% enantiomeric excess (ee)), and their vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra have been recorded. The experimental spectra are compared to theoretical spectra obtained from quantum mechanical calculations (density functional theory with the B3LYP hybrid exchange correlation functional with 6-31++G*, aug-cc-pVDZ, or aug-cc-pVTZ basis set) and related to the physical structure of the compounds. The absolute configuration could be established directly in each case by comparing experimental and theoretical spectra. In addition, we have been able to document the changes that occur both in structures and in the VA and VCD spectra due to substituent effects on the oxirane ring.     

Regioselectivity in lithiation of 1-methylpyrazole: experimental, density functional theory and multinuclear NMR study

Reaction of 1-methylpyrazole with n-BuLi in THF followed by reaction with monodeuteromethanol (CH3OD) under kinetically controlled conditions leads to functionalisation at the methyl group, whereas reaction under thermodynamically controlled conditions leads to functionalisation at the pyrazole 5-position. The observed regioselectivity can be correctly predicted, at least qualitatively, using density functional B3LYP/6-31+G(d,p) calculations only when solvation effects (IEFPCM) are taken into account. The 1H,6Li HOESY and NOESY NMR spectra of the thermodynamic product 5-lithio-1-methylpyrazole (5-Li) in [D8]THF are consistent with an oligomeric structure.     

High-spin states in 22Ne populated in the 14C(12C, α)reaction

The CDF Collaboration reported an excess in the production of two jets in association with a W . We discuss constraints on possible new particle state interpretations of this excess. The fact of no statistically significant deviation from the SM expectation for Z +dijet events in CDF data disfavors the new particle explanation. We show that the nucleon intrinsic strange quarks provide an important contribution to the W boson production in association with a single top quark production. Such W +t single top quark production can contribute to the CDF W +dijet excess, thus the nucleon intrinsic quarks can provide a possible explanation to the CDF excess in W +dijet but not in Z +dijet events.     

Structural features of muscimol, a potent GABAA receptor agonist, crystal structure and quantum chemicalab initio calculations

Muscimol, a constituent of the mushroomAmanita muscaria, is a semirigid analogue of the inhibitory neurotransmitter 4-aminobutyric acid (GABA). X-ray structure determinations and quantum chemicalab initio calculations (HF/6-31G^*) have been carried out on the muscimol zwitterion. The solid-state conformations of the muscimol zwitterion are calculated to be 1.6–2.2 kcal/mol higher in energy than that of the calculated minimum energy structurein vacuo. A comparison of the calculated and experimental structures indicates that the hydrogen bonding network in the solid state significantly affects the geometry of the molecular structure. This conclusion is supported by results ofab initio calculations on binary complexes between muscimol and an ammonium ion and between muscimol and a methoxide anion, simulating observed hydrogen bonding in the crystal structures.     

Mild and efficient nickel-catalyzed Heck reactions with electron-rich olefins

A new efficient protocol for the nickel-catalyzed Heck reaction of aryl triflates with vinyl ethers is presented. Mild reaction conditions that equal those of the corresponding palladium-catalyzed Heck reaction are applied, representing a practical and more sustainable alternative to the conventional regioselective arylation of vinyl ethers. A catalytic system comprised of Ni(COD)(2) and 1,1'-bis(diphenylphosphino)ferrocene (DPPF) in combination with the tertiary amine Cy(2)NMe proved effective in the olefination of a wide range of aryl triflates. Both electron-deficient and electron-rich arenes proved compatible, and the corresponding aryl methyl ketone could be secured after hydrolysis in yields approaching quantitative. Good functional group tolerance was observed matching the characteristics of the analogous Pd-catalyzed Heck reaction. The high levels of catalytic activity were explained by the intermediacy of a cationic nickel(II) complex potentially responsible for the successive β-hydride elimination and base promoted catalyst regeneration. Although these elementary reactions are normally considered challenging, DFT calculations suggested this pathway to be favorable under the applied reaction conditions.     

Microstructure and dynamics in lyotropic liquid crystals. Principles and applications of nuclear spin relaxation

Nuclear spin relaxation of quadrupolar nuclei provides access to a wide range of properties of lyotropic liquid crystals, ranging from the molecular ordering and dynamics at the interface to the macroscopic viscoelastic behaviour. We emphasize here the unique capability of the spin relaxation method to provide detailed geometric and dynamic information relating to the microstructure of lyotropic liquid crystals, i.e. the metric, curvature, and fluctuations of the dividing interface that separates polar and non-polar regions. This information is conveyed to the spin system via the translational diffusion of surfactants or counterions over the interface. The general principles of the spin relaxation method, as applied to lyotropic liquid crystals, are described, with emphasis on the model-independent information content of the relaxation observables and on the relation to microstructure. Specific results for lamellar, hexagonal, cubic, and nematic phases are also described.     

Modeling the stereoselectivity of the beta-amino alcohol-promoted addition of dialkylzinc to aldehydes

The title reaction has been modeled by a Q2MM force field, allowing for rapid evaluation of several thousand TS conformations. For 10 experimental systems taken from the literature, the pathway leading to the major enantiomer has been identified. Furthermore, several possible contributions to the minor enantiomer have been investigated, providing an identification of the reasons for the sometimes moderate enantioselectivity of the title reaction, and allowing for future rational improvement of existing ligands. The favored pathways to the minor enantiomer, which must be blocked for significant selectivity improvement, differ strongly among ligands. Thus, design ideas are not necessarily transferable between ligand classes, but must be developed for each reaction on the basis of the pathway that needs to be blocked in each specific case. However, we have identified some general structure-selectivity relationships.