Increase in isotopic selectivity with pressure in the multiphoton infrared decomposition of CF3Br

The C-13 isotopic selectivity in the multiphoton decomposition of CF₃Br has been shown to increase with increasing pressure of substrate for photolysis far to the red of the resonant, low intensity absorption band using relatively low fluence radiation. However, the quantum efficiency would appear to decrease as pressure is increased.     

Non-dispersive systems in atomic fluorescence spectroscopy—III : Scattering by particles and its correction in practical analysis

In the determination of trace metals in sample solutions containing high concentrations of matrix material, the usefulness of the atomic fluorescence technique may be limited by the scatter signal from particulate matter in the flame. The nature and extent of this phenomenon are investigated and various methods of correction for it are discussed. These methods are applied in several practical analyses of high-purity metals, plant materials and soil samples.     

Stereoselective synthesis of 4-hydroxy-2,3,6-trisubstituted tetrahydropyrans

[reaction: see text] Reaction of homoallylic alcohols with aldehydes in the presence of TFA gives, after hydrolysis of the ester, 4-hydroxy-2,3,6-trisubstituted tetrahydropyrans with the creation of three new stereocenters in a single-pot process. By varying the aldehyde component, a variety of functionalized side chains are installed at C-2. The utility of this approach is extended to the enantioselective synthesis of tetrahydropyrans with >99% ee.     

Intermolecular rhodium catalyzed hydroacylation of allenes: the regioselective synthesis of β,γ-unsaturated ketones

A variety of β-S-substituted aldehydes undergo efficient and regioselective rhodium catalyzed hydroacylation reactions with 1,3-disubstituted and 1,1,3-trisubstituted allenes, to deliver β,γ-unsaturated ketone products. Regioselectivites are controlled primarily by steric factors. The reactions are catalyzed by the complex [Rh(dppe)]ClO₄.     

Anisotropy of second-order nonlinear optical susceptibilities of arsenic triiodide-sulfur addition complex: AsI3 · 3S8

We report the anisotropic linear and second-order nonlinear optical (NLO) properties of arsenic triiodide-octa-sulfur (1:3) adduct, AsI₃ · 3S₈, which spontaneously crystallizes in the trigonal rhombohedral non-centrosymmetric space group R3m. The trigonal symmetry of the AsI₃ · 3S₈ molecule coincides with the crystal symmetry. The crystals are optically uniaxial with n_o/n_e of about 1.2 and show dichroism at the UV-visible wavelengths. Second harmonic generation (SHG) tensor elements were determined from Maker fringes measured with an Nd:YAG laser (∼10 ns pulse, 1064 nm). The coefficient d_222,eff = 32.0 pm/V for the light polarized parallel to the layers of iodine and sulfur atoms in the AsI₃ · 3S₈ crystal ab plane is markedly larger than d₃₃₃ = 11.6 pm/V for the polarization of light parallel to the crystal c axis. The anisotropy parameter, defined as the d_222,eff/d₃₃₃ ratio, is about 2.7 for the AsI₃ · 3S₈ crystal, smaller than that for the isomorphous CHI₃ · 3S₈ crystal (7.3) but larger than for the SbI₃ · 3S₈ crystal (0.7). Highly anisotropic components of the first hyperpolarizability tensor of an AsI₃ · 3S₈ molecule, β, were derived from the quadratic nonlinear susceptibility tensor of the crystal.