Search results for " atom"
showing 10 items of 1526 documents
Molecular squares of Ni(II) and Cu(II): ferromagnetic exchange interaction mediated by syn-anti carboxylate-bridging.
2009
The synthesis of four discrete tetranuclear complexes {[Ni(II)(L(2))][ClO(4)]}(4).MeCN (1), {[Cu(II)(L(1))(O(3)SCF(3))]}(4).H(2)O (), {[Cu(II)(L(3))(OClO(3))]}(4).MeCN () and {[Cu(II)(L(4))][ClO(4)]}(4).3MeCN.4H(2)O (4), supported by a closely similar group of carboxylate-appended (2-pyridyl)alkylamine ligands [L(1)(-): 3-[N-methyl-{2-(pyridin-2-yl)ethyl}amino]propionate; L(2)(-): 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate; L(3)(-): 3-[N-isopropyl-{2-(pyridin-2-yl)methyl}amino]propionate and L(4)(2-): 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)] is described. Structural characterization reveals that each Ni(II) centre in 1 has square-pyramidal Ni(II)N(3)O(2) …
Vergleichende Untersuchung zur Diastereoselektivität derO-Methylierung von sterisch behinderten β-Ketocarbonsäureestern und ihren Enolen
1990
Diastereoselectivity of the O-Methylation of Sterically Hindered β-Ketocarboxylates and Their Enols The enols 1a, b, and 1c, which exists almost completely in the keto form, have been methylated at the oxygen atom with diazomethane. The regioselective reaction can be catalyzed by methanol, but may loose in that case the diastereoselectivity. A comparison with the methylation of the enolates by iodomethane is discussed.
Base-Dependent Stereodivergent Intramolecular Aza-Michael Reaction: Asymmetric Synthesis of 1,3-Disubstituted Isoindolines
2013
The nucleophilic addition (A(N)) / intramolecular aza-Michael reaction (IMAMR) process on Ellman's tert-butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3-disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza-Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C2-symmetric bisacetate-substituted isoindolines. In addition, bisacetate isoindolines bearing two well-differentiated ester moieties are also noteworthy because they may a…
Quantum-chemistry calculations of surface complex and orbital control in para/ortho toluene alkylation catalyzed by big pore zeolites
1994
Summary By means of MNDO-PM3 semiempirical quantum-chemistry calculations, the mechanism for alkylation of toluene by methanol on two zeolite clusters with Al and Ga as T III has been studied. The process variables controlled through the hypersurface of the reaction were: the distances of methyl group to the cluster of zeolite and to the toluene molecule; and the distances of the hydrogen atom of the toluene to be transfered to the zeolite cluster and to the toluene. The energetic factor associated with the electronic interaction between the molecular orbitals (LUMO of the zeolite-methoxy and HOMO of toluene) have been calculated by a PMO analysis for two geometries: the transition state an…
Antimykotische wirkstoffe. XXI. Aliphatisch und alicyclisch substituierte chlor-diallylamino-1l,3,5-triazine
1988
Aus der nucleophilen Substitution eines Chloratoms in 2,4-Dichlor-6-(diallylamino)-1,3,5-triazin (1) durch Amine (2a-g) gehen die Alkylamino- und Cycloalkylamino-chlor-(diallylamino)-1,3,5-triazine (3a-g) hervor. Von den zur Untermauerung des Strukturtyps 3 herangezogenen spektroskopischen Daten sind besonders charakteristisch die durch das 1,3,5-Triazinringsystem hervorgerufene IR-Bande bei 800 cm−1, die den Allylgruppen zuzuordnenden vier 1H-NMR-Signale zwischen 4,1–6,1 ppm und das beim massenspektroskopischen Abbau auftretende Rumpfkation m/e 158. Auffallend ausgepragt sind in Verbindungsklasse 3 antimykotische, trichomonazide und herbizide Wirksamkeit. By nucleophilic substitution of on…
Polycondensed nitrogen heterocycles. Part25. Aminopyrrolo[1,2-f]-phenanthridines by decomposition of 2-(3-azidophenyl)-1-arylpyrroles
1994
Acid catalyzed decomposition of the azido derivatives 4a-c gave rise to amino-hydroxy-phenylpyrroles of type 7 and 8 upon hydrolysis of the intermediate aryl nitrenium ions, together with the hydrogen abstraction compounds of type 3. The aminopyrrolo[1,2-f]phenanthridines 10, 11, and 12 were obtained by treatment with TFMSA of the azide 4d in which the ring being attacked was made more nucleophilic by the introduction of the methoxy group.
ChemInform Abstract: Polycondensed Nitrogen Heterocycles. Part 25. Aminopyrrolo(1,2-f) phenanthridines by Decomposition of 2-(3-Azidophenyl)-1-arylpy…
2010
Acid catalyzed decomposition of the azido derivatives 4a-c gave rise to amino-hydroxy-phenylpyrroles of type 7 and 8 upon hydrolysis of the intermediate aryl nitrenium ions, together with the hydrogen abstraction compounds of type 3. The aminopyrrolo[1,2-f]phenanthridines 10, 11, and 12 were obtained by treatment with TFMSA of the azide 4d in which the ring being attacked was made more nucleophilic by the introduction of the methoxy group.
Potential energy surface for the decomposition of mandelic acid
1997
Abstract The decomposition of mandelic acid has been studied by ab initio calculations at the MP2/6-31G ∗∗ level. Three competitive reaction pathways have been characterized, two are stepwise processes with the formation of an α-lactone intermediate, achieved by the nucleophilic attack of either the carbonylic oxygen atom (mechanism A) or the hydroxylic oxygen atom (mechanism B) of the carboxyl group, followed by a ring opening; the third pathway (mechanism C) is a one-step process. The calculated rate coefficient agrees with experimental data. The decomposition is energetically favourable along mechanism A.
Kinetik der bromierung von phenolen und phenolischen mehrkernverbindungen, 2. Die reaktionsfähigkeit isomerer zweikernverbindungen
1976
Die Geschwindigkeit der Bromierung von 6 isomeren Zweikernverbindungen mit jeweils einer reaktionsfahigen Stelle (Hydroxydimethylbenzyl-methylphenole 1, 2 und 3) wurde in Eisessig bei 22°C UV-spektroskopisch bestimmt. Fur die Reaktion in ortho-Stellung zur phenolischen Hydroxy-Gruppe ergibt sich eine Verminderung der Geschwindigkeit um den Faktor 3–3,5 wenn zwischen den Hydroxy-Gruppen der beiden Phenolbausteine eine intramolekulare Wasserstoffbrucke sterisch moglich ist (1a). In den anderen Fallen (1b, 2a, 2b) verlauft die Bromierung ungefahr ebenso schnell wie bei 2,4-Dimethylphenol. Die schneller verlaufende Reaktion in para-Stellung (3a, 3b) wird durch eine Wasserstoffbrucke um den Fakt…
Low-lying Rydberg states of HCl.
2008
Vertical excitation energies belonging to some different Rydberg series of hydrogen chloride have been determined with a coupled-cluster theoretical approach. These excitation energies have allowed us to calculate electric dipole transition intensities in HCl and allow additional assessment of the calculation approach presently used to provide an adequate description of the valence and Rydberg states of HCl. The molecular quantum defect orbital has been applied to the calculation of oscillator strengths. In particular, new insight is given on the assignment of states as the R1Pi, the 1Delta(4dpi and 5ppi), the 1Sigma+(4dpi), and the nddelta(1Pi, 1Phi) and 4f states.