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81.
Pyridines have been formed by heating azabicyclo[3.2.0]hept-2-en-4-ones in toluene. The generation of a 3-azacyclopentadienone intermediate via a [2 + 2]-cycloreversion is proposed as the key step. A Diels-Alder reaction of a styrene, extrusion of carbon monoxide, and loss of hydrogen then gives the pyridine. The process parallels the well-known synthesis of benzenes from cyclopentadienones. The azabicyclo[3.2.0]hept-2-en-4-ones were synthesized from the reaction between readily available cyclopropenones and 1-azetines, in which the cyclopropenones behave as all-carbon 1,3-dipolar equivalents. 相似文献
82.
Assessments accompanying published textbooks: the extent to which mathematical processes are evident
Patricia D. Hunsader Denisse R. Thompson Barbara Zorin Amanda Loyden Mohn Jennifer Zakrzewski Ilyas Karadeniz Elaine C. Fisher George MacDonald 《ZDM》2014,46(5):797-813
Assessments accompanying published textbooks are often used by teachers in the USA as a primary means to evaluate students’ mathematical knowledge. In addition to assessing content knowledge, assessments should provide insight into students’ ability to engage with mathematical processes such as reasoning, communication, connections, and representations. We report here an analysis of the extent to which the assessments accompanying published textbooks in the USA at the elementary, middle grades, and high school levels provide opportunities for students to engage with these mathematical processes. Results indicate that in elementary grades, communication, connections, and graphics are not consistently emphasized across grade levels and publishers. In middle grades, students are rarely asked to record their reasoning or translate among representational forms of a concept. In high school geometry, students are given many opportunities to interpret and create graphics, but the same is not true for algebra. With the exception of connections, the results suggest that inconsistent emphasis is placed on the mathematical processes within assessments accompanying commercial textbooks in the USA. 相似文献
83.
Sonia Zulfiqar Muhammad Rafique Muhammad Sajjad Shaukat Muhammad Ishaq Muhammad Ilyas Sarwar 《Colloid and polymer science》2009,287(6):715-723
Nanocomposites from organoclay and aromatic polyamide were prepared using solution intercalation method. Aramid chains were
synthesised by reacting 4-aminophenylsulfone with isophthaloyl chloride in dimethylacetamide. Dodecylamine was used as a modifier
to change the hydrophilic nature of montmorillonite into organophilic. Suitable quantities of organoclay were mixed in the
aramid solution with high-speed stirring for homogeneous dispersion of the clay. Thin films cast from these materials after
evaporating the solvent were characterised. The morphology of nanocomposites was determined by X-ray diffraction and TEM.
Results revealed the formation of delaminated and disordered intercalated clay platelets in the aramid matrix. Mechanical
data indicated improvement in the tensile strength and modulus with clay loading up to 6 wt.%. The glass transition temperature
increased up to 20 wt.% organoclay, suggesting better cohesion between the two phases and thermal stability augmented with
increasing clay loading. The water uptake reduced gradually as a function of organoclay showing decreased permeability. 相似文献
84.
Amir H. Mohammadi Ilyas Kraouti Dominique Richon 《The Journal of chemical thermodynamics》2009,41(6):779-782
In this communication, experimental data for dissociation conditions of methane hydrates in the presence of 0.05 and 0.1 mass fractions NaBr, KBr, K2CO3, and MgCl2 aqueous solutions and in the presence of 0.05 and 0.15 mass fractions CaBr2 aqueous solutions are reported. The experimental data were generated using an isochoric pressure-search method. The new experimental dissociation data for methane hydrates in the presence of 0.1 mass fraction MgCl2 aqueous solution are compared with some selected experimental data from the literature and the agreements are generally found acceptable. Some of new data are finally compared with the predictions of a correlation, which is generally used in the absence of experimental data, and acceptable agreements between the experimental and predicted data are observed. 相似文献
85.
Syed Zafar Ilyas S.M. Nasir Yuksel Kaplan 《Mathematical and Computer Modelling》2009,50(9-10):1495-1497
A Gaussian trend for humidity versus temperature is confirmed by a theoretical fit, i.e., where T0 and H0 are the experimental values of the temperature and humidity, respectively and K is a constant. 相似文献
86.
[reaction: see text] Transition structures have been located for oxygen transfer from performate anion to ethylene, propene, vinylamine, vinyl chloride, vinyl cyanide, and 2-propen-1-ol at the B3LYP/6-31+G(d,p) level in a CPCM continuum model for water. Oxygen transfer is concerted, except for acrylonitrile, which is stepwise. Peracid anions react as ambiphilic oxygen donors. Predictions are made about the diastereoselectivity of epoxidations of acylic, chiral, and allylic alcohols in an alkaline solution, and one is verified experimentally. 相似文献
87.
Ebner S Wallfisch B Andraos J Aitbaev I Kiselewsky M Bernhardt PV Kollenz G Wentrup C 《Organic & biomolecular chemistry》2003,1(14):2550-2555
Flash vacuum thermolysis (FVT) of 1-(dimethylamino)pyrrole-2,3-diones 5 causes extrusion of CO with formation of transient hydrazonoketenes 7. The transient ketenes 7 are observable in the form of weak bands at 2130 (7a) or 2115 cm-1 (7b) in the Ar matrix IR spectra resulting from either FVT or photolysis of either 5 or 1,1-dimethylpyrazolium-5-oxides 8, and these absorptions are in excellent agreement with B3LYP/6-31G* frequency calculations. Under FVT conditions the ketenes 7 cyclize to pyrazolium oxides 8, which undergo 1,4-migration of a methyl group to yield 1,4-dimethyl-3-phenylpyrazole-5(4H)-one 9a and 1,4,4-trimethyl-3- phenylpyrazole-5(4H)-one 9b. All three tautomers of 9a have been characterized, viz. the CH form 9a (most stable form in the gas phase, the solid state and solvents of low polarity), the OH form 9a' (metastable solid at room temperature) and the NH form 9a" (stable in aprotic dipolar solvents). The isomeric 1,4-dimethyl-5-phenylpyrazole-3(2H)- one 12 tautomerizes to the 3-hydroxypyrazole 12'. The crystal structure of the hydrochloride 14 of 9a'/9a" is reported, representing the first structurally characterised example of a protonated 5-hydroxypyrazole. 相似文献
88.
Wave functions have been determined for the C2H4PH and C2H4S cyclic molecules, using (951/52/3) and (95/52/3) uncontracted Gaussian basis sets for each molecule. From Mulliken population analyses and electron-density plots, it is shown that the valence orbitals of C2H4PH and C2H4S are closely related and that these are similar to the respective orbitals of cyclopropane.
Zusammenfassung Für die zyklischen Moleküle C2H4PH und C2H4S wurden mit den nichtkontrahierten Basissätzen ((951/52/3) und (95/52/3)) von Gaußfunktionen Wellenfunktionen bestimmt. Die Mullikenschen Populationsanalysen sowie Diagramme der Elektronendichte zeigen, daß die Valenzorbitale von C2H4PH und C2H4S in enger Beziehung stehen und daß diese den entsprechenden Orbitalen des Cyclopropans ähnlich sind.相似文献
89.
90.