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Isomeric Mixture (isomeric + mixture)
Selected AbstractsHighly Selective Iridium-Catalyzed Asymmetric Hydrogenation of Trifluoromethyl Olefins: A New Route to Trifluoromethyl- Bearing StereocentersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Mattias Engman Abstract Fluorine-containing compounds are useful in many applications ranging from pharmaceuticals to ferroelectric crystals. We have developed a new, highly enantioselective synthetic route to trifluoromethyl-bearing stereocenters in up to 96% ee via asymmetric hydrogenation using N,P-ligated iridium catalysts. We also hydrogenated an isomeric mixture of olefins; this reaction gave the hydrogenation product highly enantioselectively (87% ee), and only the E isomer was present after the reaction had reached 56% conversion. [source] Synthesis of soluble branched polyimides derived from an ABB, monomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2004Kun-Li Wang Abstract A novel ABB, monomer, an isomeric mixture of 4-[4-(2,4-diaminophenoxy)phenoxy]phthalic acid 2-methyl ester, was successfully prepared. The direct polycondensation of the ABB, monomer was carried out to form polyamic acid monomethyl ester as a precursor with an inherent viscosity of 0.30 dL/g and a number-average molecular weight of 12,000. The degree of branching of the precursor, determined by 1H NMR, was 0.07. The low degree of branching was caused by the differences in the reactivities of the amino groups. The shape factor was calculated to be 0.72. End-modified reactions with acetyl chloride, benzoyl chloride, and phthalic anhydride were carried out. After the chemical imidization of the end-modified precursors, end-modified polyimides were successfully prepared. The end-modified polyimides were soluble in dimethyl sulfoxide, dimethylformamide (DMF), and N -methyl-2-pyrrolidinone. On the basis of thermogravimetry and differential scanning calorimetry measurements of the polyimides, the 5 wt % thermal loss temperatures were determined to be 400,520 °C, and the glass-transition temperatures were determined to be 200,258 °C. According to the X-ray diffraction measurements, the end-modified polyimides were amorphous. A strong but brittle film was prepared from an acetamide end-modified polyimide solution, via casting from a DMF solution, with a tensile strength of 46 MPa, an elongation at break of 4%, and a modulus of 1.3 GPa. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3200,3211, 2004 [source] Isolation and antimicrobial evaluation of isomeric hydroxy ketones in leaf cuticular waxes of Annona squamosa,PHYTOCHEMICAL ANALYSIS, Issue 1 2007K. Shiva Shanker Abstract A novel natural compound, 11-hydroxy-16-hentriacontanone, has been isolated from the leaf cuticular wax of Annona squamosa along with its known isomer 10-hydroxy-16-hentriacontanone in a ratio of 67:33. This isomeric mixture of hydroxy ketones constituted together 16.5% of the total cuticular waxes. The new compound was characterised using spectral and chromatographic techniques. The major component was found to be 16-hentriacontanone (palmitone), which constituted up to 48% of the total cuticular wax, together with a homologous series of hydrocarbons, fatty aldehydes, fatty alcohols, fatty acids and sterols as minor components. The antimicrobial activity of the isomeric hydroxy ketones was tested against selected Gram-positive and Gram-negative bacterial strains, and also some selected fungal strains, and compared with palmitone. The antibacterial activity of palmitone was significantly higher than that of the isomeric hydroxy ketones, but their antifungal activities were comparable. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of the separation of aziridine isomers applying heptakis(2,3-di- O -methyl-6-sulfato),-CD and heptakis(2,3-di- O -acetyl-6-sulfato),-CD in aqueous and nonaqueous systemsELECTROPHORESIS, Issue 20 2005Yaser Bitar Abstract Aziridines are attracting interest as protease inhibitors, which might be used, e.g., for treatment of parasitic diseases. Within the framework of greater projects dealing with the search of new selective protease inhibitors, a huge number of aziridines with two stereogenic centers will be synthesized. Thus, a fast and reliable screening method for the evaluation of the isomeric composition is needed. Robust baseline separations were obtained using heptakis(2,3-di- O -acetyl-6-sulfato),-CD (HDAS) in acidic methanol and sulfated ,-CD in acidic phosphate buffer. With HDAS the resolutions were higher and migration times shorter. Thus, the method will be used as a screening method for further isomeric mixtures of aziridines. [source] | ||||||||||