Search results for "yield"
showing 10 items of 1338 documents
Divulging the various chemical reactivity of trifluoromethyl-4-vinyl-benzene as well as methyl-4-vinyl-benzene in [3+2] cycloaddition reactions.
2020
Abstract In the present paper, an investigation about the [3 + 2]cycloaddition (32 C A) reactions of benzonitrile oxide with 1-trifluoromethyl-4-vinyl-benzene, and with 1-methyl-4-vinyl-benzene, using the Molecular Electron Density Theory (MEDT) through DFT/B3LYP/6–311++G (d,p), is performed. A deep mechanistic study beside an accurate electronic description of different stationary points along the IRC paths of the two 32 C A reactions have performed by examining the two competitive regioisomericortho/metareaction pathways, and providing the mechanism associated with them. The presence of the CF3 group reduces the activation energy, which makes it possible to increase the experimental yield…
Osmium(III) Complexes with POP Pincer Ligands: Preparation from Commercially Available OsCl3·3H2O and Their X-ray Structures
2010
Complexes OsCl3{dbf(PiPr2)2} [1; dbf(PiPr2)2 = 4,6-bis(diisopropylphosphino)dibenzofuran], OsCl3{xant(PiPr2)2} [2; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene], and OsCl3{xant(PPh2)2} [3; xant(PPh2)2 = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene] have been obtained in high yield by the reaction of the corresponding diphosphine with OsCl3·3H2O. The ruthenium(III) counterparts RuCl3{dbf(PiPr2)2} (4), RuCl3{xant(PiPr2)2} (5), and RuCl3{xant(PPh2)2} (6) are similarly obtained from RuCl3·3H2O in moderate yields. The X-ray structures of dbf(PiPr2)2 and complexes 1−3 are also reported.
On the Intrinsic Population of the Lowest Triplet State of Thymine
2007
The population of the lowest triplet state of thymine after near-UV irradiation has been established, on the basis of CASPT2//CASSCF quantum chemical calculations, to take place via three distinct intersystem crossing mechanisms from the initially populated singlet bright 1pipi* state. Two singlet-triplet crossings have been found along the minimum-energy path for ultrafast decay of the singlet state at 4.8 and 4.0 eV, involving the lowest 3npi* and 3pipi* states, respectively. Large spin-orbit coupling elements predict efficient intersystem crossing processes in both cases. Another mechanism involving energy transfer from the lowest 1npi* state with much larger spin-orbit coupling terms ca…
Blends of PDMS and random copolymers of dimethylsiloxane and methylphenylsiloxane: Phase separation in the quiescent state and under shear
1999
The miscibility of random copolymers (COP), consisting of dimethylsiloxane and methylphenylsiloxane units, with poly(dimethylsiloxane)s (PDMS) was studied in the absence and in the presence of shear experimentally as well as theoretically. Blends of COP 0.86 28 with PDMS 33 (subscripts: volume fraction of DMS in the copolymer, numbers after the abbreviations: weight average molar masses in kg/mol) were investigated far from critical conditions on the PDMS side of the phase diagram. According to these experiments the two phase regime increases by shear without exception and the maximum effects grow from 3 to 12 K as the PDMS concentration increases. Theoretical calculations were performed un…
Nebenreaktionen der radikalisch ausgelösten Cyclisierung von 2,2′-Methylen-bis(4-methyl-1,2-phenylen)-dimethacrylat
1979
2,2′-Methylene-bis(4-methyl-1,2-phenylene) dimethacrylate (1) was reacted with an excess of 2,2′-azoiso-butyronitrile (mole ratio 1:15) highly diluted in boiling benzene. The reaction products were separated by column chromatography. It was found that the 1-cyano-1-methylethyl radical induced the cyclization of 1 to yield the product of a head to tail addition (2) in 55% yield. In addition, the product of a head to head addition (3) was isolated in 4% yield. 35% of 1 reacted in the same way as it has already been observed as suppression of polymerization in the case of p-tolyl methacrylate to give the products 4 and 5. The structures of the products were confirmed by elemental analyses, by …
General Equilibrium Models of Monopolistic Competition: CRRA Versus CARA
2005
We analyze a class of "large group" Chamberlinian monopolistic competition models using multiplicatively quasi-separable (MQS) and additively quasi-separable (AQS) functions. We first prove that the MQS and AQS functions are equivalent to the "constant relative risk aversion" (CRRA) and "constant absolute risk aversion" (CARA) classes of functions, respectively. Whereas both approaches allow for closed-form solutions, only the AQS functions yield profit-maximizing prices that decrease in the mass of competing firms. We then characterize the equilibrium in both cases and discuss some possible applications of the AQS framework to trade, growth, and development.
Essential oil variation within and among natural populations of Lavandula latifolia and its relation to their ecological areas
2007
Essential oil yield and composition in seven natural populations of Lavandula latifolia from the eastern Iberian Peninsula were determined by GC/MS. Twenty-eight constituents were identified, accounting for 92.0e95.4% of the total oils. These oils were dominated by the monoterpene fraction and three of them (linalool, cineole and camphor) constituted 79.5e86.9% of the oil from flowers. Essential oil yield in leaves and flowers varied among and within populations, but hierarchic analyses of variance showed that the proportion of variation attributable to individuals was significantly higher than that attributable to population differences. Principal component and cluster analyses allowed thr…
Enantioselective Synthesis of (−)-Dihydrocodeine and Formal Synthesis of (−)-Thebaine, (−)-Codeine, and (−)-Morphine from a Deprotonated α-Aminonitri…
2014
The α-benzylation of a deprotonated bicyclic α-aminonitrile, followed by Noyori's asymmetric transfer hydrogenation combined with the Grewe cyclization onto a symmetrical A-ring precursor, are the key steps of a short and high-yielding enantioselective synthesis of the morphinan (-)-dihydrocodeine. This compound can be converted to (-)-thebaine in high yield by known transformations, while (-)-codeine and (-)-morphine are available from an advanced intermediate.
Highly luminescent perovskite–aluminum oxide composites
2015
In this communication we report on the preparation of CH3NH3PbBr3 perovskite/Al2O3 nanoparticle composites in a thin film configuration and demonstrate their high photoluminescence quantum yield. The composite material is solution-processed at low temperature, using stable alumina nanoparticle dispersions. There is a large influence of the alumina nanoparticle concentration on the perovskite morphology and on its photoluminescence.
Application of molecular topology for the prediction of the reaction times and yields under solvent-free conditions
2010
Ball milling and conventional magnetic stirring can be used to support different laboratory techniques with a highly efficient mixing of reagents under solvent-free conditions. By using multilinear regression and linear discriminant analysis, topological-mathematical models have been built to predict the yield and the reaction time for organocatalytic reactions, Suzuki reactions and reactions of synthesis of heterocyclic compounds. The results from the in silico predictions confirm the usefulness of the approach followed.