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Atoms
Kinds of Atoms Terms modified by Atoms Selected AbstractsThe all-too-flexible abductive method: ATOM's normative status,JOURNAL OF CLINICAL PSYCHOLOGY, Issue 9 2008Jan-Willem Romeijn Abstract The author discusses the abductive theory of method (ATOM) by Brian Haig from a philosophical perspective, connecting his theory with a number of issues and trends in contemporary philosophy of science. It is argued that as it stands, the methodology presented by Haig is too permissive. Both the use of analogical reasoning and the application of exploratory factor analysis leave us with too many candidate theories to choose from, and explanatory coherence cannot be expected to save the day. The author ends with some suggestions to remedy the permissiveness and lack of normative force in ATOM, deriving from the experimental practice within which psychological data are produced. © 2008 Wiley Periodicals, Inc. J Clin Psychol 64:1,14, 2008. [source] Cyclopenta[a]quinolizine: A Novel Pseudoazulene with a Bridgehead Nitrogen AtomEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 28 2010Pavel V. Gormay Abstract Cyclopenta[a]quinolizine, a novel tricyclic pseudoazulene, was prepared by reaction of cyclopentadienyllithium with oxazolo[3,2- a]pyridinium or substituted pyridinium salts. Structural analysis (X-ray analysis, NMR and UV spectroscopy) and DFT calculations confirm its highly dipolar nature (due to delocalization of the negative charge around the five-membered ring) combined with partial localization of bonds in both six-membered rings. [source] Synthetic Potentials of Heptamethine Merocyanine Dyes Containing an Active Chlorine Atom: Reactivity towards NucleophilesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2009Tzveta Gospodova Abstract The reactivity of heptamethine merocyanine dyes that contain an active chlorine atom at a meso position of the polymethine chain towards nucleophiles is investigated for the first time. The reactivity differs completely from that of cationic cyanine dyes and is consistent with a concerted SNAr addition,elimination mechanism. This mechanism is additionally supported by the performed DFT calculations in the gas phase and in solution. The observed dependence of the reaction on the type of the nucleophilic agents is discussed in terms of Pearson's theory. Additional diversification of and improvement in the stability of the ramified merocyanines is achieved in reactions with methyl-substituted quaternary salts of nitrogen-containing heterocycles. The photophysical characteristics of the novel dyes are reported and compared with those of the parent merocyanine.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Synthesis and Enzymic Hydrolysis of Oligoribonucleotides Incorporating 3-Deazaguanosine: The Importance of the Nitrogen-3 Atom of Single Conserved Guanosine Residues on the Catalytic Activity of the Hammerhead RibozymeHELVETICA CHIMICA ACTA, Issue 8 2003Frank Seela Four base-modified hammerhead ribozyme/substrate complexes were constructed in which single guanosine (1) residues were replaced by 3-deazaguanosine (2) in the positions G5, G8, GL2.1, and G12. The base-modified ribozyme complexes were prepared by solid-phase synthesis of oligoribonucleotides employing the novel phosphoramidite 3 derived from 2. Phosphoramidite 3 carried a phenoxyacetyl group at the amino function and a diphenylcarbamoyl residue at the oxo group of the nucleobase. The 2,-hydroxy group was blocked with a triisopropylsilyl residue. Kinetic analysis of the phosphodiester hydrolysis showed a moderate decrease of the ribozyme catalytic activity when the residues G5 or G8 were replaced by 3-deazaguanosine and a 200-fold decrease when G12 was substituted. A 6-fold catalytic increase occurred when 3-deazaguanosine was replacing GL2.1 in the loop region. The data indicate that the N(3) atom of compound 2, in particular at position G12 is critical for the ribozyme activity. [source] Atom,atom partitioning of total (super)molecular energy: The hidden terms of classical force fieldsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2007M. Rafat Abstract Classical force fields describe the interaction between atoms that are bonded or nonbonded via simple potential energy expressions. Their parameters are often determined by fitting to ab initio energies and electrostatic potentials. A direct quantum chemical guide to constructing a force field would be the atom,atom partitioning of the energy of molecules and van der Waals complexes relevant to the force field. The authors used the theory of quantum chemical topology to partition the energy of five systems [H2, CO, H2O, (H2O)2, and (HF)2] in terms of kinetic, Coulomb, and exchange intra-atomic and interatomic contributions. The authors monitored the variation of these contributions with changing bond length or angle. Current force fields focus only on interatomic interaction energies and assume that these purely potential energy terms are the only ones that govern structure and dynamics in atomistic simulations. Here the authors highlight the importance of self-energy terms (kinetic and intra-atomic Coulomb and exchange). © 2006 Wiley Periodicals, Inc. J Comput Chem 2007 [source] Einzelne Atome im optischen ResonatorPHYSIK IN UNSERER ZEIT (PHIUZ), Issue 1 2006Axel Kuhn Die kontrollierte Kopplung von einzelnen Atomen und Photonen gewinnt zunehmend an Bedeutung. Garchinger Forschern ist es jetzt gelungen, ein Atom in einem winzigen Resonator mehr als 15 Sekunden lang so zu platzieren, dass es auf ein einziges darin zirkulierendes Photon reagieren kann. Außerdem konnten sie das Atom in einem Laserfeld mit einer Genauigkeit von 135 nm verschieben. [source] Exploring the Reactivity of Carbon(0)/Borane-Based Frustrated Lewis Pairs,ANGEWANDTE CHEMIE, Issue 33 2010Manuel Alcarazo Dr. Doppelt frustriert: Die ungewöhnliche elektronische Verteilung um das zentrale Kohlenstoff(0)-Atom in Carbodiphosphoranen macht dieses Zentrum so basisch, dass es selbst nach einem ersten Alkylierungsschritt dazu in der Lage ist, als kationische Lewis-Base im Rahmen der Chemie frustrierter Lewis-Paare zu wirken. [source] Carben-Übergangsmetallkomplexe durch zweifache C-H-BindungsaktivierungANGEWANDTE CHEMIE, Issue 28 2010Helmut Werner Prof. Abstract Die Aktivierung einer einzelnen sp3 -C-H-Bindung von Alkanen und ihren Derivativen durch elektronenreiche Übergangsmetallkomplexe wurde seit den 1982 erschienenen bahnbrechenden Arbeiten von Bergman und Graham zu einem viel bearbeiteten Forschungsprojekt. Zehn Jahre später wurde gezeigt, dass Verbindungen der 5d-Elemente, z.,B. von Osmium und Iridium, auch zu einer zweifachen ,-C-H-Bindungsaktivierung von Alkan- oder Cycloalkanderivaten fähig sind, sofern diese eine funktionelle Gruppe wie OR oder NR2 besitzen. Damit war ein neuer Zugang zu Carbenkomplexen der Übergangsmetalle vom Fischer-Typ eröffnet. Nachfolgende Arbeiten konzentrierten sich zuerst auf die Umwandlung von Alkyl(methyl)- und Aryl(methyl)ethern in Oxocarben- und von Dimethylaminen in Aminocarbenliganden. Kürzlich wurde gezeigt, dass so hergestellte quadratisch-planare Oxocarbeniridium(I)-Komplexe zu einem ungewöhnlichen Reaktivitätstyp befähigt sind. Sie reagieren mit CO2,, CS2,, COS, PhNCO und PhNCS gemäß einer Atom- oder Gruppentransfermetathese, für die es bisher kein Beispiel gibt. Organoazide RN3 und N2O verhalten sich ähnlich. Jüngste Ergebnisse weisen darauf hin, dass solche Metathesereaktionen auch katalytisch durchgeführt werden können, wodurch sich eine neue Möglichkeit zur Funktionalisierung von C-H-Bindungen bietet. [source] 2,5-Bis(p -R-arylethynyl)rhodacyclopentadienes Show Intense Fluorescence: Denying the Presence of a Heavy Atom,ANGEWANDTE CHEMIE, Issue 13 2010Andreas Steffen Dr. Schwermetall-Lichtshow: Photophysikalische Untersuchungen ergaben für eine Reihe von Rhodiumkomplexen unerwartet hohe Fluoreszenzquantenausbeuten (,f bis 69,%, ,f,1,3,ns) und ein unerwartet langsames Intersystem-Crossing. Diese neue Verbindungsklasse hinterfragt das gängige Modell zum Verhalten angeregter elektronischer Zustände und zur Rolle von Schweratomen in Intersystem-Crossing-Prozessen. THF=Tetrahydrofuran, Tol=Toluol. [source] Elektronendichteverteilung in einem Metallaphosphan,ANGEWANDTE CHEMIE, Issue 13 2010Julian Henn Dr. Bereit zum Brückenschlag: Das Metallaphosphan [Me2Al(,-Py)2P] enthält ein zweiwertiges PIII -Atom, das laut Elektronendichtestudien zwei freie Elektronenpaare trägt. Dieser Befund erklärt, dass das Phosphoratom im sekundären Phosphan PPy2(H) ,-verbrückend zu zwei {W(CO)5}-Einheiten im freien zweikernigen Komplex [{(OC)5W}2(,-P)Py2(H)] (siehe Bild; lila P, gelb W, blau N, rot O, schwarz C) eingesetzt werden kann und sich wie ein Vier-Elektronen-Donor verhält. [source] Isothiourea-Catalyzed Enantioselective Carboxy Group Transfer,ANGEWANDTE CHEMIE, Issue 47 2009Caroline Joannesse Von Atom zu Atom: Enantiomerenreine Isothioharnstoffe vermitteln den hoch selektiven Transfer der Carboxygruppe vom O- auf das C-Atom in Oxazolylcarbonaten (siehe Schema). Die Enantioselektivität dieses Prozesses wurde mechanistisch untersucht und mithilfe von Rechnungen erklärt. [source] Hypervalent Carbon Atom: "Freezing" the SN2 Transition State,ANGEWANDTE CHEMIE, Issue 35 2009Simon Fünf gewinnt! Unter bestimmten Umständen liegen hypervalente Kohlenstoffatome mit fünf Substituenten in einer trigonal-bipyramidalen Anordnung vor (siehe Struktur), die dem normalerweise labilen Übergangszustand von SN2-Reaktionen entspricht. [source] ChemInform Abstract: One-Pot Synthesis of Internal Conjugated (Z)-Enynyltrimethylsilanes Possessing Aryl, Cycloalkenyl, (E)- or (Z)-Alk-1-enyl Moieties on the sp Carbon Atom via Two Types of Cross-Coupling Reaction.CHEMINFORM, Issue 13 2009Masayuki Hoshi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: Unexpected Effect of the Fluorine Atom on the Optimal Ligand-to-Palladium Ratio in the Enantioselective Pd-Catalyzed Allylation Reaction of Fluorinated Enol Carbonates.CHEMINFORM, Issue 47 2008Etienne Belanger Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] ChemInform Abstract: A Design Concept of Long-Wavelength Fluorescent Analogues of Rhodamine Dyes: Replacement of Oxygen with Silicon Atom.CHEMINFORM, Issue 33 2008Meiyan Fu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] Synthesis and Structures of Pyrimidinophanes Containing a Nitrogen Atom in the Bridge.CHEMINFORM, Issue 52 2006V. E. Semenov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Arboflorine, an Unusual Pentacyclic Monoterpenoid Indole Alkaloid Incorporating a Third Nitrogen Atom.CHEMINFORM, Issue 36 2006Kuan-Hon Lim Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] First Example of the Mislow,Braverman,Evans Rearrangement Retaining the Sulfur Atom on the Original Carbon.CHEMINFORM, Issue 26 2006Tsuyoshi Satoh Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] A C,C Bond Formation Reaction at the ,-Carbon Atom of ,-Oxo Ketene Dithioacetals via the Baylis,Hillman Type Reaction.CHEMINFORM, Issue 40 2005Yan-Bing Yin Abstract For Abstract see ChemInform Abstract in Full Text. [source] Lewis Acid Mediated Diastereoselective Reduction of N-Protected ,-Amino Ketones: Influence of the Nature of the Metal Atom and of the Nitrogen Protecting Group.CHEMINFORM, Issue 37 2004Giuseppe Bartoli Abstract For Abstract see ChemInform Abstract in Full Text. [source] Recyclization of 5-Ethoxycarbonylpyrimidines Occurring with Substitution of a Carbon Atom in the Heterocycle by an Exocyclic Carbon Atom.CHEMINFORM, Issue 34 2004G. G. Danagulyan Abstract For Abstract see ChemInform Abstract in Full Text. [source] Steric Effects in the Nucleophilic Addition of Pyrazoles Unsubstituted at a Nitrogen Atom to the Double Bond of Maleic Anhydride.CHEMINFORM, Issue 33 2004N. L. Nam Abstract For Abstract see ChemInform Abstract in Full Text. [source] Heterocyclic Systems Containing Bridgehead Nitrogen Atom: Synthesis and Bioactivity of 3-(2-Thienyl)-s-triazolo[3,4-b][1,3,4]thiadiazole (IV), 2-(2-Thienyl)thiazolo[3,2-b]-s-triazole (XII) and Isomeric 3-(2-Thienyl)-thiazolo[2,3-c]-s-triazole (IX).CHEMINFORM, Issue 22 2003Jag Mohan No abstract is available for this article. [source] New Condensed Heterocyclic System (III) with a Bridgehead Phosphorus Atom.CHEMINFORM, Issue 52 2002V. V. Ivanov No abstract is available for this article. [source] ChemInform Abstract: Enhanced Leaving Ability of Methoxy Group and Retarded Deprotonation on the Carbon Atom Linked to the 1-Position of 8-Phosphino- or 8-Amino-naphthalene.CHEMINFORM, Issue 33 2002Akio Toshimitsu 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] ChemInform Abstract: A Straightforward Synthesis of Some Fused Aza-Arenes via Nucleophilic Displacement of a Ring Hydrogen Atom in Nitroarenes by Aromatic Hydrazone Anions.CHEMINFORM, Issue 30 2002Koji Uehata 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] ChemInform Abstract: Silylation of Silyl- and Germylketenes Containing Bulky Substituents at the Silicon or Germanium Atom.CHEMINFORM, Issue 7 2002S. V. Ponomarev 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] ChemInform Abstract: Crown Ethers with Azo or Azoxy Unit and Sulfur Atom(s) in 16-Membered Macrocycle.CHEMINFORM, Issue 44 2001J. Szczygelska-Tao 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] ChemInform Abstract: Ruthenium-Catalyzed Regioselective ,-Alkylation of Ketones: The First Alkyl-Group Transfer from Trialkylamines to the ,-C Atom of Ketones.CHEMINFORM, Issue 24 2001Chan Sik Cho 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] ChemInform Abstract: Heterocyclic Systems Containing Bridgehead Nitrogen Atom: Synthesis and Bioactivity of Thiazolo[3,2-b]-s-triazoles and Isomeric Thiazolo[2,3-c]-s-triazoles.CHEMINFORM, Issue 23 2001Jag Mohan 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] | |||||||||||||||||||||||||||||||||||||||||||