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  • 1
    Electronic Resource
    Electronic Resource
    Heterocyclic Betaines. 20. Unconventional Extended .pi.-Systems Containing Imidazolium (Pyridinium) and Benzimidazolate Subunits. Synthesis and Structural Aspects (1994)
    s.l. : American Chemical Society
    The @journal of organic chemistry 59 (1994), S. 644-648 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00082a024
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  • 2
    Electronic Resource
    Electronic Resource
    Isocyanides as hydrogen bond acceptors (1998)
    Springer
    Theoretical chemistry accounts 99 (1998), S. 116-123 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Hydrogen bonds ; Isocyanides ; Atoms in molecules methodology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. A theoretical study of the capability of hydrogen isocyanide (HNC) as a hydrogen bond acceptor has been carried out. The geometry, interaction energy and electronic properties of the corresponding complexes with HF, HCl, HBr, H2O, NH3, HCCH, HCN and HNC itself indicate that it is able to form strong hydrogen bonds. A search in the Cambridge Structural Database has shown the presence of isocyanides involved in hydrogen bonds in solid phase. Finally, the comparison of the properties of HNC with its isomer, hydrogen cyanide, shows strong similarities between both compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050313
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  • 3
    Electronic Resource
    Electronic Resource
    Bond Length–Electron Density Relationships: From Covalent Bonds to Hydrogen Bond Interactions (1998)
    Springer
    Structural chemistry 9 (1998), S. 243-247 
    Details
    ISSN: 1572-9001
    Keywords: Hydrogen bonds ; electron density ; bond critical points ; DFT calculations ; Pauling's bond order ; bond length
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is possible to treat bond distances of covalent C-H bonds and C⋯H hydrogen bonds simultaneously assuming a logarithmic relationship with the electron density at the bond critical point. Similar relationships have been found for other X-H/X⋯H bonds. The data used for obtaining these equations have been determined theoretically. All the systems have been fully optimized and their electron densities calculated at the B3LYP/6-311 + + G(d,p) level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022424228462
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of 1,2,6-thiadiazine 1,1-dioxides (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 470-476 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio theoretical calculations were carried out on the three tautomers, NH, OH and CH, of 1,2,6-thiadiazine 1,1-dioxides. Different basis sets were employed in order to obtain an adequate description of these cyclic sulphamide derivatives. A coherent picture is obtained which includes relative stability of tautomers (NH 〉 CH 〉 OH), non-planarity of NH and CH tautomers and electronic distribution (Boys' localized orbitals).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030709
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  • 5
    Electronic Resource
    Electronic Resource
    Comparative study of aromaticity in five-membered rings containing S, SO and SO2 groups (1992)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 74-82 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Owing to the importance of the concept of aromaticity, different indices have been developed to try to quantify this property. The possible π delocalization through an X—SOn—X group (X = C, N; n = 0, 1 or 2) could explain heteroaromaticity in rings containing the moiety. For that reason, the aromaticity of five-membered sulphurcontaining rings with different oxidation numbers (S, SO and SO2) and including no (thiophene), one (isothiazole) or two (1,2,5-thiadiazole) adjacent atoms was investigated. Ab initio calculations were carried out to determine geometrical parameters (planarity of the ring, bond length and bond order), electronic structure (charge distribution and dipolar moment) and the participation of d-orbitals of sulphur. According to these calculations, only compounds with S(II) can be considered to be aromatic, whereas compounds bearing S(IV) or S(VI) are better described as ylides.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610050203
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  • 6
    Electronic Resource
    Electronic Resource
    Atomic charges derived from different methods: A comparative study applied to SO2 heterocycles (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 477-487 
    Details
    ISSN: 0020-7608
    Keywords: charge derivation at ab initio level ; charge distribution election ; dipole moment ; electronegativity ; SO2 heterocycles ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Atomic charges were calculated at ab initio level using different methods of charge determination to compare them and estimate their utility in the electronic description of heterocycles containing the SO2 moiety. Those procedures implemented on the Gaussian92 program were included [Mulliken population analysis, Weinhold-Reed natural population analysis (NPA) and CHELPG]. The first two are based on the molecular orbitals while in the third one the charges are derived by fitting the electrostatic potential. Two sets of compounds were chosen to represent the different characteristics of the SO2 heterocycles studied: simpler five-member heterocycles and SO2 small derivatives. These molecules were optimized at the HF/6-31G* level and their energy evaluated by a punctual calculation MP2/6-31G*//HF/6-31G*. The dipole moments for these molecules were obtained by using all the methods previously mentioned and compared with the SCF, MP2, and experimental dipole moments. The influence on the charges of some atoms by changing the electronegativity of neighboring atoms has also been investigated for these compounds. The results obtained show that the best methods to describe the electronic distribution of the oxathiole studied are Mulliken and CHELPG at the MP2 level of calculation. The charge distributions obtained with these two methods for these particular heterocycles are discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 477-487, 1997
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    On the inhibition of alcohol dehydrogenase: Shape group analysis of molecular electrostatic potential on van der Waals surfaces for some pyrazole derivatives (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 269-288 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assessment of molecular similarity between molecules is a fundamental task in computer-aided drug design. In this work, we have applied a combined analysis of steric and electrostatic properties of a series of inhibitors of liver alcohol dehydrogenase (LADH) to rationalize their action. The methodology is based on a topological characterization of the distribution of molecular electrostatic potential (MEP) on the fused-sphere van der Waals surface of a molecule. The topological description can be rendered in the form of two-dimensional diagrams that allow a quick visual or algorithmic analysis of the most relevant shape features of a molecule. By using the representations mentioned above (topological information as a function of the MEP), one can correlate this “structural” information with the values of inhibition constants KI for compounds with different levels of inhibitory activity. This approach allows one to have quantitative measures of similarity for related molecules and to eventually propose compounds that may exhibit a desired activity. The compounds analyzed in this work are a series of substituted derivatives of pyrazole, which span a relatively wide range of inhibitory powers. We have studied the role of the nature of the substituent, as well as its substitutional position, on the molecular shape and correlated these findings with the activity of each compound. Some consequences on the mechanism of inhibition of LADH are also discussed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400725
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  • 8
    Electronic Resource
    Electronic Resource
    On the Tautomerism of 2-Phenacyl-4-pyrimidinones and Related Compounds (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 919-924 
    Details
    ISSN: 0009-2940
    Keywords: Pyrimidinones ; Tautomerism ; AM1 calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zur Tautomerie von 2-Phenacyl-4-pyrimidinonen und verwandten Verbindungen3-Methyl-2-phenacyl-4-pyrimidinone 1, 2 werden durch Sulfidkontraktion synthetisiert. Aufgrund der NMR-Daten existieren die Verbindungen ausschließlich in der Benzoylmethylen-Form, sowohl in Lösung als auch als Festkörper. Diese Ergebnisse werden durch AM1-Berechnungen für die Stammverbindung bestätigt. Die Untersuchung des Tautomeren-Gleichgewichts mittels dieser semiempirischen Methode wurde auf andere Fälle von Enaminoketon/Enolimin-Tautomerie erweitert.
    Notes: 3-Methyl-2-phenacyl-4-pyrimidinones 1, 2 have been synthesized using the sulfide contraction. According to the NMR data, the compounds 1, 2 exist exclusively as the benzoylmethylene tautomers a both in solution and in the solid state. AM1 calculations of the parent system are in agreement with the experimental observations. The study of the tautomeric equilibrium by this semiempirical method has been extended to other cases of enamino-ketone/enolimine tautomerism.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220521
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  • 9
    Electronic Resource
    Electronic Resource
    15N and 13C NMR spectroscopy of 1,2,6-thiadiazine 1,1-dioxide derivatives and fused systems (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 444-450 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural abundance 15N NMR spectra of sulphamide, sixteen 1,2,6-thiadiazine and two 1,2,4,6-thiatriazine derivatives, phenylbutazone and antipyrine have been recorded for the first time. The influence of substituents on nitrogen chemical shifts and the effect of intercalation of SO2 and CO groups between two nitrogen atoms are discussed. Prototropic tautomerism was also studied. 13C NMR data for some of the 1,2,6-thiadiazine and thiatriazine derivatives are reported.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240511
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  • 10
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    Inverse Hydrogen-Bonded Complexes (1997)
    American Chemical Society
    Details
    Publication Date: 1997-06-01
    Print ISSN: 1089-5639
    Electronic ISSN: 1520-5215
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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