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Insertion Process (insertion + process)
Selected AbstractsChemInform Abstract: Catalytic Asymmetric Synthesis of 1,1,-Spirobi[indan-3,3,-dione] via a Double Intramolecular C,H Insertion Process.CHEMINFORM, Issue 52 2001Teruki Takahashi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Insertion Reactions of 1,2-Disubstituted Olefins with an , -Diimine Palladium(II) ComplexHELVETICA CHIMICA ACTA, Issue 8 2006Carla Carfagna Abstract The migratory insertions of cis or trans olefins CH(X)CH(Me) (X,=,Ph, Br, or Et) into the metal,acyl bond of the complex [Pd(Me)(CO)(iPr2dab)]+ [B{3,5-(CF3)2C6H3}4], (1) (iPr2dab,=,1,4-diisopropyl-1,4-diazabuta-1,3-diene,=,N,N, -(ethane-1,2-diylidene)bis[1-methylethanamine]) are described (Scheme,1). The resulting five-membered palladacycles were characterized by NMR spectroscopy and X-ray analysis. Experimental data reveal some important aspects concerning the regio- and stereochemistry of the insertion process. In particular, the presence of a Ph or Br substituent at the alkene leads to the formation of highly regiospecific products. Moreover, in all cases, the geometry of the substituents in the formed palladacycle was the same as in the starting olefin, as a consequence of a cis addition of the Pd,acyl fragment to the CC bond. Reaction with CO and MeOH of the five-membered complex derived from trans-, -methylstyrene (=,[(1E)-prop-1-enyl]benzene) insertion, yielded the 2,3-substituted , -keto ester 9 with an (2RS,3SR)-configuration (Scheme,3). [source] A Density Functional Study of Ethylene Insertion into the M-methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3,ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002Kumar Vanka Single site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium-carbon chain for contact ion-pair systems of the type [L1L2TiCH3 -,-CH3 -B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the ,-CH3 bridge were considered. The counterion, B(C6F5)3CH3,, was modeled by QM/MM methods. The value of ,Htot,the total barrier to insertion,was found to be positive (in the range of 4,15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion-pair was found to be an important factor in determining the value of ,Htot. On replacing the titanium metal center with zirconium, the ,Htot values were found to be lowered (in the range of 2,9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ,Htot was found to increase (in the range of 10,28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ,Htot. Solvent effects were incorporated with cyclohexane (, = 2.023) as the solvent, and were found to have a minor influence, ±(0.5,1.5) kcal/mol) on the insertion barrier for all the cases studied. [source] Spectrophotometric Analysis of Tooth Color Reproduction on Anterior All-Ceramic Crowns: Part 2: Color Reproduction and Its Transfer from In Vitro to In VivoJOURNAL OF ESTHETIC AND RESTORATIVE DENTISTRY, Issue 1 2010AKI YOSHIDA RDT ABSTRACT Color reproduction of an anterior tooth requires advanced laboratory techniques, talent, and artistic skills. Color matching in a laboratory requires the successful transfer from in vivo with careful considerations. The purpose of this study was to monitor and verify the color reproduction process for an anterior all-ceramic crown in a laboratory through spectrophotometric measurements. Furthermore, a crown insertion process using composite luting cements was assessed, and the final color match was measured and confirmed. An all-ceramic crown with a zirconia ceramic coping for the maxillary right central incisor was fabricated. There was a significant color difference between the prepared tooth and the die material. The die material selected was the closest match available. The ceramic coping filled with die material indicated a large color difference from the target tooth in both lightness and chromaticity. During the first bake, three different approaches were intentionally used corresponding with three different tooth regions (cervical, body, and incisal). The first bake created the fundamental color of the crown that allowed some color shifts in the enamel layer, which was added later. The color of the completed crown demonstrated an excellent color match, with ,E 1.27 in the incisal and 1.71 in the body. In the cervical area, color match with ,E 2.37 was fabricated with the expectation of a color effect from the underlying prepared tooth. The optimal use of composite luting cement adjusted the effect from the underlying prepared tooth color, and the color match fabricated at a laboratory was successfully transferred to the clinical setting. The precise color measurement system leads to an accurate verification of color reproduction and its transfer. CLINICAL SIGNIFICANCE The use of a dedicated dental spectrophotometer during the fabrication of an all-ceramic crown allows the dentist and the laboratory technician to accurately communicate important information to one another about the shade of the tooth preparation, the shade of the contralateral target tooth, and the influence of luting cement on the final restoration, thereby allowing the technician better control over the outcome of their tooth color matching efforts and the final color match of an all-ceramic restoration. (J Esthet Restor Dent 22:53,65, 2010) [source] Copper T380A intrauterine device for emergency contraception: a prospective, multicentre, cohort clinical trialBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 10 2010S Wu Please cite this paper as: Wu S, Godfrey E, Wojdyla D, Dong J, Cong J, Wang C, von Hertzen H. Copper T380A intrauterine device for emergency contraception: a prospective, multicentre, cohort clinical trial. BJOG 2010;117:1205,1210. Objective, To determine the effectiveness of the Copper T380A (CuT380A) intrauterine device (IUD) as an emergency contraceptive in women. Design, Prospective, multicentre, cohort clinical trial. Setting, Eighteen family planning clinics in China. Sample, A cohort of 1963 women, aged 18,44 years, requesting emergency contraception within 120 hours of unprotected sexual intercourse. Methods, Women requesting emergency contraception were followed at 1, 3 and 12 months after the insertion of CuT380A. Main outcome measures, Efficacy of CuT380A as emergency contraception and for up to 12 months of postinsertion use. Insertion complication rates, reported side-effects and continuation rates at 12 months were also recorded. Results, No pregnancies occurred prior to or at the first follow-up visit, making CuT380A 100% effective as emergency contraception in this study. The pregnancy rate over the 12-month period was 0.23 per 100 women. In all, 29 (1.5%) women experienced a difficult IUD insertion process, requiring local anaesthesia or prophylactic antibiotics. No uterine perforations occurred. The main side-effects were increased menstrual bleeding and menstrual disturbances. The 12-month postinsertion continuation rate was 94.0 per 100 woman-years. Conclusions, CuT380A is a safe and effective method for emergency contraception. The advantages of CuT380A include its ability to provide effective, long-term contraception. [source] A furnace for in situ X-ray diffraction studies of insertion processes in electrode materials at elevated temperaturesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2001T. Eriksson A furnace is described for in situ X-ray diffraction studies, in transmission mode, of structural changes in electrode materials for Li-ion (polymer) batteries in the ambient to 300°C temperature range. The method exploits the thin flat-cell geometry of the lithium-polymer battery concept. The flat sample is able to oscillate about a horizontal axis in its own plane in the X-ray beam, to provide better averaging during the diffraction experiment. The use of the device is demonstrated in a study of lithium intercalation in graphite (a commonly used anode material in lithium-ion batteries) during electrochemical cycling and storage at 70°C. [source] Catalytic activity during the preparation of PE/clay nanocomposites by in situ polymerization with metallocene catalystsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Paula Zapata Abstract Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay-supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay-supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA-intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAO-treated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA-intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] | |||||||||||||