Effect of Anchimeric Assistance in the Reaction of Triphenylphosphine with α,β‐Unsaturated Carboxylic Acids

Quaternization of triphenylphosphine with maleic and cis‐aconitic acids is strongly accelerated by participation of the cis‐carboxyl group in stabilization of the phosphonium zwitterion intermediate by intramolecular hydrogen bonding, in spite of steric hindrance by the acid's reaction center. A similar effect for trans‐isomeric acids is not observed, which can be rationalized on the basis of spatial structures of the generated zwitterions, implying an electrostatic interaction between the phosphonium center and carbonyl oxygen atom. The effect of anchimeric assistance decreases when the intramolecular hydrogen bonding disfavors attack of the phosphine on the sterically less hindered carbon atom of the C=C bond, as observed for cis‐aconitic acid.     

Monotonicity in confined system problems

When an atom is confined at the center of a spherically symmetric impenetrable sphere, the electron density is altered. Of particular interest are the changes in the electron density at the center of the cavity as they affect important physical properties such as the isotropic constants of the hyperfine structure. This work presents four simple theorems that facilitate understanding the behavior of the electron density of the ground state with variations in the potential or in the radius of the impenetrable spherical cavity. The general statements are illustrated by discussion of the known results for confined and free systems and the results of simple evaluations for model hydrogen-like atoms in a cavity.     

Influence of pH of solution on phase composition of samarium-strontium cobaltite powders synthesized by wet chemical technique

Powders of Sm_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.

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A novel polybromide complex of bismuth – (Et4N)3{[Bi2Br9](Br2)}: synthesis and structural features

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Effective stereoselective approach to substituted 1,4-dioxane-2,5-diones as prospective substrates for ring-opening polymerization

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Synthesis of tritium-labeled PAM-43

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Synthesis and electrochemical study of 2-carbamoyl-4,5-dihydro-1,3,4-thiadiazole-containing ligands and their complexes with Cuii, Coii and Niii

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The Henry reaction catalyzed by zeolitic imidazolate framework ZIF-8

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