Applications of 1,4-addition of grignard reagents to α,β-unsaturated acid derivatives. III—configuration studies of α,β-diaryl-α,β-dialkylpropionitriles

The configuration of twenty-four different α,β-diaryl-α,β-dialkylpropionitriles has been determined using nuclear magnetic resonance spectra. The erythro form showed greater deshielding of the methine hydrogen and alkyl groups in its spectra than the corresponding threo isomer. The former, however, showed less deshielding of the aryl groups than the threo isomer. Infrared spectra were not suitable for assignments of configuration.     

Stereoselective synthesis of functionalized precursors of the CDEF and CDE 2,6-dideoxy-tetra- and trisaccharide units of durhamycins A and B

[structure: see text] Highly stereoselective syntheses of functionalized precursors of the CDEF and CDE 2,6-dideoxy-tetra- and trisaccharide units of the anti-HIV aureolic acids durhamycins A and B using 2-deoxy-2-iodo- and 2-deoxy-2-bromopyranosyl donors are described.     

Structure of chlorohydroxonitrosyl(terpyridine)ruthenium(II) hexafluorophosphate

The title complex has the NO grouptrans to the hydroxyl ligand and the chloride ion in the plane of the tripyridyl ligand. The Ru−O and Ru−N(O) distances are 1.939(5) ? and 1.764(6) ?, respectively; the Ru−N−O bond angle is 171.7(6)⁰. These values are consistent with previously reported shortening of Ru−O distances whentrans to a linear NO ligand. The space group of the structure isP2₁/c, witha=9.7213(9) ?,b=13.9318(11) ?,c=14.523(4) ?, and β=105.820(13)⁰.     

Radionuclide concentrations in two sewage treatment plants on Western Lake Ontario,Canada

Radionuclide concentrations in digester sludge and effluent samples from Hamilton and Dundas sewage treatment plants, located at the western tip of Lake Ontario, have been determined by high-resolution γ-ray spectrometry. The radionuclides⁵¹Cr,⁷⁵Se and¹³¹I, which are used in nuclear medicine procedures, were found in sludge samples. Very low concentrations of⁵¹Cr, entering Lake Ontario through the Hamilton plant effluent discharge, have little effect on lake water quality.     

Polymerization of aromatic nuclei. XVII. Catalytic hydrogenation of poly(p-phenylene)

Hydrogenation of poly(p-phenylene) (I) in cyclohexane at high temperature and pressure with rhodium catalyst gave, in low yield, oligomers of 1,4-cyclohexylene(II) in the range of 2–16 cyclohexyl units per chain. Apparently only the low molecular weight fraction in I is reduced because of extreme insolubility. II, which appears to be a novel class, was characterized by molecular weight, ¹H-NMR, ¹³C-NMR, and infrared spectra, gas chromatography, and microanalyses. Dicyclohexyl and perhydro-p-sexiphenyl served as model compounds for comparison in characterization of II.     

Feedback control of canards

We present a control mechanism for tuning a fast-slow dynamical system undergoing a supercritical Hopf bifurcation to be in the canard regime, the tiny parameter window between small and large periodic behavior. Our control strategy uses continuous feedback control via a slow control variable to cause the system to drift on average toward canard orbits. We apply this to tune the FitzHugh-Nagumo model to produce maximal canard orbits. When the controller is improperly configured, periodic or chaotic mixed-mode oscillations are found. We also investigate the effects of noise on this control mechanism. Finally, we demonstrate that a sensor tuned in this way to operate near the canard regime can detect tiny changes in system parameters.     

The ordering of crystallographic shear planes: Theory of regular arrays

In certain non-stoichiometric transition metal oxides, crystallographic shear planes are found instead of isolated oxygen vacancies. These planes tend to form arrays with regular spacings. The interactions responsible for this ordering have not been understood in the past. We propose that the major interaction comes from elastic strain, with smaller electrostatic terms: the configuration of the planes is one which minimises the elastic strain energy. Quantitative results are given for a realistic model, and agree with the main features observed experimentally. Thus the regular array of planes is stable, and the equilibrium separation of planes in the array is about half that predicted for an isolated pair of planes. The interaction between isolated planes proves an oscillatory function of their separation. One can understand from its detailed form why the observed mean spacing gets smaller as the planes come together to form larger groups.