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  • 1
    Electronic Resource
    Electronic Resource
    Relative energies of the C2H2S2 isomers 1,2-dithiete and dithioglyoxal: Peculiar basis set dependencies of density functional theory and ab initio methods (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 8430-8433 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio calculations at the levels of Hartree–Fock (HF), second order Møller–Plesset perturbation theory (MP2), coupled-cluster theory with singles, doubles, and estimated triple excitations [CCSD(T)], and density functional theory (DFT) using the functionals B3LYP and B3PW91 of the relative energies of the C2H2S2 isomers 1,2-dithiete (2a), and dithioglyoxal (2b) show a peculiar dependence of the results on the f-type polarization functions. The ab initio calculations with 6-31G(nd) basis sets with n=1–3 incorrectly predict that 2a is higher in energy than 2b. The relative energies at the MP2 and CCSD(T) levels change by more than 6 kcal/mol in favor of 2a if the basis set is augmented by one set of f functions. The DFT calculations also give a higher stability of 2a relative to 2b if f functions are included in the basis sets, but the change in the relative energy is only ∼2 kcal/mol. The large change in the relative energies which are calculated at MP2 and CCSD(T) are mainly due to the functions at sulfur, while the effect of the f functions in the DFT calculations is mainly due to the f functions at carbon. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318749
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanism of carbon dioxide elimination from ionized methyl haloacetates in the gas phase. Formation of CH3XCH2+.cntdot. and CH3XCHX+.cntdot. (X = Cl, Br) halonium radical ions (1983)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 105 (1983), S. 2186-2193 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00346a015
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  • 3
    Electronic Resource
    Electronic Resource
    Chemistry Another noble gas conquered (2000)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 406 (2000), S. 836-837 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] On page 874 of this issue Khriachtchev et al. report the synthesis of the first compound containing the noble gas argon. This leaves only two stable elements in the periodic table — helium and neon — for which no neutral compound exists. But the experimental strategy that was ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35022678
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical ab initio Study of TiCl4 Ammonolysis: Gas Phase Reactions of TiN Chemical Vapor Deposition (2000)
    Springer
    Journal of molecular modeling 6 (2000), S. 413-424 
    Details
    ISSN: 0948-5023
    Keywords: Keywords Titanium nitride, Ab initio calculations, Chemical vapor deposition, Ammonolysis, Donor-acceptor complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The mechanism of TiCl4 ammonolysis has been studied theoretically at ab initio Hartree-Fock, B3LYP, MP2 and CCSD(T)//B3LYP levels using effective core potentials for Ti and Cl and 6-31G* basis sets for N and H. TiCl4 and products of its ammonolysis form five- and six-coordinated complexes with ammonia, which intermediate substitution of Cl atoms by NH2 groups. Transition state energies for the subsequent steps of ammonolysis decrease with increasing number of NH2 groups bound to Ti. The energy of the transition state for the first step of ammonolysis is 19 kcal mol-1 above the energy of the reactants (TiCl4+NH3) and 8 kcal mol-1 above the products (TiCl3NH2 + HCl). The following steps have transition states energetically located below the products, indicating weak hydrogen bonded complex formation as intermediate between transition state and product. A thermodynamic estimation shows the last step of ammonolysis to be endothermic, while the first three steps are exothermic if the adduct formation energy is taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010740
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  • 5
    Electronic Resource
    Electronic Resource
    Transformation matrices as tool to investigate the changes in the electronic structure of reacting molecules along the reaction coordinate (1984)
    Springer
    Theoretical chemistry accounts 65 (1984), S. 65-76 
    Details
    ISSN: 1432-2234
    Keywords: Transformation matrix ; electronic structure of transition states ; orbital interaction ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The calculation of the transformation matrix between the molecular orbitals of the transition state and the educt provides detailed information on the alteration and interaction of the MO’s along the reaction coordinate. This is demonstrated for four different kinds of reactions: (a) Conrotatory ringopening of cyclobutene; (b) Addition of methylene to ethylene; (c) Nucleophilic substitution of CH3CN and CH3NC by CN−; (d) 1,2 Rearrangement of methylcarbene to ethylene. MNDO has been employed for the calculations but any other method may be used as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427581
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  • 6
    Electronic Resource
    Electronic Resource
    Transformation matrices as tool to investigate the changes in the electronic structure of reacting molecules along the reaction coordinate (1984)
    Springer
    Theoretical chemistry accounts 65 (1984), S. 65-76 
    Details
    ISSN: 1432-2234
    Keywords: Transformation matrix ; electronic structure of transition states ; orbital interaction ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The calculation of the transformation matrix between the molecular orbitals of the transition state and the educt provides detailed information on the alteration and interaction of the MO's along the reaction coordinate. This is demonstrated for four different kinds of reactions: (a) Conrotatory ringopening of cyclobutene; (b) Addition of methylene to ethylene; (c) Nucleophilic substitution of CH3CN and CH3NC by CN−; (d) 1,2 Rearrangement of methylcarbene to ethylene. MNDO has been employed for the calculations but any other method may be used as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00552300
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  • 7
    Electronic Resource
    Electronic Resource
    Perspective on “Wechselwirkung neutraler Atome und homöopolare Bindung nach der Quantenmechanik” (2000)
    Springer
    Theoretical chemistry accounts 103 (2000), S. 177-179 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Covalent bond – Hydrogen molecule – Helium atom – Noncrossing rule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The paper of Heitler and London was the first quantum theoretical study which explains the nature of the covalent bond. It also contains the noncrossing rule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002149900040
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  • 8
    Electronic Resource
    Electronic Resource
    Perspective on “Quantentheoretische Beiträge zum Benzolproblem. I. Die Elektronenkonfiguration des Benzols und verwandter Beziehungen” (2000)
    Springer
    Theoretical chemistry accounts 103 (2000), S. 187-189 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Aromaticity – Molecular orbital theory – Valence bond theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Guided by an intuitive choice of approximations which shows remarkable chemical insight into the topic of aromaticity, Hückel mastered the difficult mathematical treatment of a complex molecule like benzene at a very early stage of quantum theory using method 1 (now valence bond theory) and method 2 (now molecular orbital theory). He concluded that method 2 is clearly superior to method 1 because the results of this method explain directly the peculiar behaviour of planar molecules with 6 π electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002149900023
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  • 9
    Electronic Resource
    Electronic Resource
    Reaktivität von 1-Cyclopropen-1-carbonsäurelactonen in Abhängigkeit von der Größe des Lactonringes (1982)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 115 (1982), S. 2826-2835 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactivity of 1-Cyclopropene-1-carboxylic Acid Lactones Dependent on the Size of the Lactone RingThe reaction of the bicyclic γ-lactone 1 with KOtBu leads to lactone 3 by addition of tert-butoxide at the 1-position of the intermediate cyclopropene lactone 2 and subsequent exo-protonation. In contrast, the δ-lactone 13, readily available from cinnamyl bromide 4 in five steps, gives the tert-butoxylactones 15a and b, formed by addition to the nonisolable lactone 17 in 2-position. The ε-lactone 14 reacts analogously to give 16a and b, however, in that case also the strained cyclopropene lactone 18 can be isolated. MINDO/3 calculations show that mainly steric rather than electronic effects are responsible for this different behavior.
    Notes: Während bei der Reaktion des bicyclischen γ-Lactons 1 mit KOtBu durch Addition an das intermediäre Cyclopropenlacton 2 in der 1-Stellung und anschließende exo-Protonierung das Lacton 3 entsteht, ergibt das aus dem Cinnamylbromid 4 leicht in fünf Stufen erhältliche δ-Lacton 13 die tert-Butoxylactone 15a und b, die durch Addition an das nicht faßbare Lacton 17 in 2-Stellung gebildet werden. Das ε-Lacton 14 reagiert analog zu 16a und b, jedoch ist daneben auch das gespannte Cyclopropenlacton 18 isolierbar. MINDO/3-Rechnungen zeigen, daß dieses unterschiedliche Verhalten überwiegend auf sterische und weniger auf elektronische Gründe zurückzuführen ist.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19821150814
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  • 10
    Electronic Resource
    Electronic Resource
    Dissoziative Ringöffnung halogensubstituierter Methylcyclopropan-Radikalkationen in der Gasphase (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 1084-1094 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dissociative Ring Opening of Halogen Substituted Methylcyclopropane Cation Radicals in the Gas PhaseThe unimolecular gas phase reactions of several C4H7Br+· isomers are investigated. Rearrangement of the incipient C4H7+ ion is observed prior to Br· loss from all C4H7Br+· isomers except ionised 2- (9) and 3-methylallyl- (10) and cyclobutylbromides (6). This is evidenced by the increased average kinetic energy release associated with Br· elimination. In addition, the structure of the C4H7+ ions may be established using collisional activation spectroscopy. Ionised 1- and 2-methylcyclopropylbromides both yield 1-methylallyl cation rather than 2-methylallyl cation. MNDO calculations on the analogous C4H7Cl+· isomers lead to similar conclusions; moreover, these calculations shed light on the probable mechanism for both isomerization and decomposition of the molecular ions.
    Notes: Die unimolekularen Zerfälle einiger isomerer C4H7Br+·-Verbindungen werden in der Gasphase studiert. Die Br·-Abspaltung aus ionisiertem Cyclobutylbromid (6) und 2- bzw. 3-Methylallylbromid (9 bzw. 10) erfolgt ohne Isomerisierung des entstehenden C4H7+-Ions. Bei allen übrigen Verbindungen ist die dissoziative Ionisation mit einer Isomerisierung des Kations verbunden. Diese Umlagerung, die vor der eigentlichen Br·-Eliminierung eintritt, manifestiert sich in einer Linienverbreiterung der Übergangssignale („kinetic energy release“). Die resultierenden C4H7+-Kationen lassen sich anhand ihrer Stoßaktivierungsspektren charakterisieren. Aus den Radikalkationen der 1- und 2-Methylbromcyclopropane entsteht bei der Br·-Abspaltung das 1-Methylallylkation und nicht das 2-Methylallylkation. MNDO-Rechnungen für die analogen C4H7Cl+·-Radikalkationen unterstützen die bei den Bromiden gemachten experimentellen Befunde; außerdem enthüllen diese Rechnungen mechanistische Details der unimolekularen Reaktionen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130327
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