ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    What Governs the Stereochemistry of the SN2′ Reaction? (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1593-1597 
    Details
    ISSN: 0947-3440
    Keywords: SN2′ reaction ; Stereochemistry ; Calculations, ab initio ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations of negatively charged symmetrical and unsymmetrical transition states of the SN2′ reaction indicate that due to electronic reasons and particularly Coulomb interactions the anti transition state is generally more stable than the syn transition state. The experimentally often observed syn preference results mainly from the interaction with a polar solvent and/or the gegenion, which gives rise to higher stabilization of the syn transition state than of the anti transition state.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961015
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Zum anomeren Effekt bei Dithiatriazinen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2123-2127 
    Details
    ISSN: 0009-2940
    Keywords: 1λ4,3λ4-Dithiatriazines ; Calculations, MNDO ; Anomeric effect ; Electron diffraction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Anomeric Effect in DithiatriazinesFrom (CF3CN3S2)n (1) and XeF2, Br2, or (CF3)2NO* the corresponding S,S-substituted dithiatriazines CF3CN3S2F2 (2), CF3CN3S2Br2 (3), and CF3CN3S2[ON(CF3)2]2 (4) are prepared. An electron diffraction study of 2 in the gas phase results in a slightly aplanar 6-membered ring with chair conformation and both S-F bonds in axial position. MNDO calculations show that the position of the substituents at the sulfur atoms is strongly dependent on these substituents and on the ring geometry. The cis preference is the result of an anomeric effect.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231107
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Chlorthiatriazine (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2601-2607 
    Details
    ISSN: 0009-2940
    Keywords: Thiatriazines, trichloro, preparation, structures ; Calculations, MNDO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ChlorothiatriazinesFrom (ClSN)3 (1) and ClCN (2) 1,3,5-trichloro-1,3,2,4,6-dithiatriazine (ClCN)(ClSN)2 (3) was prepared in 26% yield. 3 reacts slowly further with excess 2 to give thiatriazine (ClCN)2(ClSN) (14) and triazine (ClCN)3 (16). A mechanism for the (ClSN)/(ClCN) exchange is proposed. The structures of 3, 14, and 16 have been determined by X-ray diffraction. The bonding situation in the system (ClSN)n(ClCN)3-n (n = 0 - 3) is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931261207
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Fluorthiatriazine (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1347-1352 
    Details
    ISSN: 0009-2940
    Keywords: 1α4,2,4,6-Thiatriazines, preparation, structures ; 1α4,2,4,6-Thiatriazinium cations ; Calculations, MNDO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: FluorothiatriazinesFrom the reaction of (ClCN)2(ClSN) (1) with AgAsF6 in liquid SO2 (ClCN)2(SN)⊕ AsF⊖06 (2) is obtained in quantitative yield. With CsF 2 gives (ClCN)2(FSN) (3), which slowly dismutates at room temperature to form (ClCN)(FCN)(FSN) (4) and 1. Fluorination of 1 with SbF3 yields (FCN)2(FSN) (5). With AsF5 5 forms the salt (FCN)2(SN)⊕ AsF⊖ (6). The cation of 6 is transformed by NOCl or CsBr into the corresponding neutral derivatives (FCN)2(ClSN) (7) and (FCN)2(BrSN) (8), respectively. The gas-phase structure of 5 was determined by electron diffraction. The influence of the different exocyclic substituents on the bond properties in this ring system is explained by means of MNDO calculations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240606
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Addition von Alkenen an 5-(Trifluormethyl)-1,3,2,4,6-dithiatriazin (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 39-45 
    Details
    ISSN: 0009-2940
    Keywords: 1,3,2,4,6-Dithiatriazines ; CNS Polycycles, structure determination ; Calculations, MNDO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition of Alkenes to 5-(Trifluoromethyl)-1,3,2,4,6-dithiatriazinesDechlorination of 1,3-dichloro-5-(trifluoromethyl)-1,3,2,4,6-dithiatriazine (1) with Ph3Sb gives (CF3CN3S2)n (2) in quantitative yield. By 1,3-addition of alkenes (dicyclopentadiene, cyclopentene, cis- and trans-2-butene, propene, and ethene) to 2 the corresponding penta- (4a), tri-(5a), and bicyclic ring systems 6a, 6b, 7, 8a, 8b, and 9 are prepared in 65-85% yields. The molecular structures of 6a and 7 were determined by single-crystal X-ray analysis; the other structures were derived from NMR data. The NMR analyses are in accordance with MNDO calculations. For 4a and 5a only the thermodynamically favoured anti-isomers are found, as expected from these calculations; for 6 and 8 they show satisfactory agreement for anti/syn-proportions as determined by NMR spectroscopy. The product distribution corresponds to a symmetry-allowed alkene addition to a singlet dithiatriazine.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240107
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Orbital Theory of Heterolytic Fragmentation and Remote Effects on Nitrogen Inversion Equilibria (1972)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 55 (1972), S. 893-906 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From a molecular orbital study of model systems we derive the electronic requirements for the Grob fragmentation. The necessary condition for an allowed fragmentation in an X-C1-C2-C3-N system, or the amino cation +C1-C2-C3-N is the level ordering A below S. This in turn is set by maximal through-bond coupling of the empty cation orbital and the nitrogen lone pair. The conformational dependence of through-bond coupling is exactly that derived by Grob, namely parallel orientation of the cation orbital (or the C-X bond), the C2-C3-σ-bond, and the N-lone-pair. When the C1-C2-C3 and C2-C3-N angles are small, the through-space interaction dominates, reversing the level ordering to S below A, and consequently makes the fragmentation forbidden even though the conformational requirements for it are met. Ring closure becomes allowed. Some examples exploiting this result are presented, as well as procedures for enhancing through-bond coupling and thus fragmentation. The through-bond-effect has also kinetic consequences, allowing the definition of a new type of remote neighbouring group participation operative through bonds and not by direct overlap. The position of equilibria in nitrogen inversion processes should also be influenced by remote substituents which are π-acceptors or donors.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19720550315
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    NMR-Spectroscopic Assignment of the Aib-Methyl Groups in α-Helical and β-Turn Environment with the Use of Selectively Deuterated Aib The Solution Conformations of Boc-Ala-Aib-Ala-OMe (1989)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 1017-1027 
    Details
    ISSN: 0170-2041
    Keywords: α-Aminoisobutyric acid ; Molecular dynamics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: NMR-spektroskopische Zuordnung der Aib-Methylgruppen in α-helikaler und β-Turn-Umgebung mit Hilfe von selektiv deuterierter Aib. - Die Konformationen von Boc-Ala-Aib-Ala-OMe in LösungBoc-Ala-Aib-Ala-OMe (1a) nimmt im Kristall eine β-turn-Typ-II-ähnliche Konformation ein. Aus 13C-CP-MAS-Spektren erhält man eine magnetische Nichtäquivalenz der Aib-Cβ-Atome von 6.1 ppm. Das pro-S-Cβ-Kohlenstoff-Signal ist nach hohem Feld verschoben, wie man durch Vergleich mit den Spektren von Boc-Ala-(R)-Aib[D1]-Ala-OMe (1b) zeigen kann. Diese Zuordnung entspricht der gefundenen Tieffeldverschiebung des pro-S-Cβ-Kohlenstoffs von Aib in der Helix von Boc-[L-Glu(OBzl)]4-Aib[L-Glu(OBzl)]7-O-PEG-M (2a, in der sie mit Hilfe des (R)-Aib[D3] enthaltenen Analogons (2b) belegt wurde. Aus Moleküldynamik-Simulationen leiten wir zwei Hauptkonformationsräume für Boc-Ala-Aib-Ala-OMe in Lösung ab, die die beobachtete MNE von 2.1 ppm, die Amid-Temperaturkoeffizienten, die Kopplungskonstanten und die aus ROESY-Spektren berechneten Abstände erklären.
    Notes: Boc-Ala-Aib-Ala-OMe (1a) adopts in the crystal a conformation similar to a β-turn type II. From 13C-CP-MAS spectra the magnetic nonequivalence of the Aib-Cβ atoms amounts to 6.1 ppm. The pro-S-Cβ carbon signal is shifted upfield as can be shown by comparison with the spectra of Boc-Ala-(R)-Aib[D1]-Ala-OMe (1b). This assignment corresponds to a downfield shift of the Aib pro-S-Cβ carbon in the helix of Boc-[L-Glu(OBzl)]4-Aib-[L-Glu(OBzl)]7-O-PEG-M (2a), where it was established with the aid of the (R)-Aib[D3]-containing analog (2b), From molecular dynamics simulations of Boc-Ala-Aib-Ala-OMe we propose two major conformational species in solution that account for the observed MNE of 2.1 ppm, the temperature gradients of the amide protons, the coupling constants, and the distances derived from ROESY spectra.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198919890260
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...