Library

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
    Medium Ring Compounds. XXIX. Cyclooctane-1,5-dione-dioxime (1976)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 1417-1423 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of the title compound (orthorhombic a = 26.724, b = 10.899, c = 9.483 Å, space group Pna21, Z = 12) has been determined by X-ray analysis. The structural units consist of hydrogen-bonded trimers with approximate C3h symmetry. The results are discussed in relation to the Beckmann rearrangement of the title compound, which yields exclusively the mirror-symmetric diamide.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19760590502
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Studies on the Conformation of Boc-Protected (S)-(+)-Isovaline Homopeptide Methyl Esters in the Solid State and in Solution (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1697-1710 
    Details
    ISSN: 0947-3440
    Keywords: Helical structures ; Circular dichroism ; Peptides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: X-Ray diffraction analyses of the fully protected peptides Boc-[(S)-Iva]n-OMe (n = 3, 4, 6) reveal two independent molecules in the asymmetric unit. The structures of these can be described as β-turns or 310 helices (depending on the length of the oligopeptide) of alternating screw sense (M and P) in a head to tail alignment. This structure is stabilized by hydrogen bonds between the N—H(1) of the (M)-helix and the O=C(ω-1) of the (P)-helix and the N—H(2) (M) and the ester carbonyl group (P). Low temperature 1H-NMR spectra of the hexamer in CD2Cl2 solution show two interchanging species in a ratio of 4:1; NOESY experiments prove that these are the two helical conformers found in the crystal (P:M, 4:1). The NOESY spectrum at -90°C indicates the pairing of (P) and (M) helices. Thermodynamic and kinetic parameters for the helix transformation P ⇌ M (unfolding/folding) are presented.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970811
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    An Eclipsed C(sp3)-CH3 Bond in a Crystalline Hydrated Tricyclic Orthoamide: Evidence for C—H…O hydrogen bonds (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 1125-1135 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Accurate, low-temperature (81 K) X-ray analyses have been made for two crystalline modifications of the tricyclic orthoamide 1b: a cubic trihydrate in space group Pa3 (Z = 8), where the molecule has crystallographic threefold rotation symmetry, and an anhydrous monoclinic form in space group P21/c (Z = 8) where two symmetry-independent molecules have different configurations, one ail-trans. (as in the cubic trihydrate), the other cis, cis, trans. In the cubic trihydrate, each orthoamide molecule is attached to a triad of H2o molecules by OH…N H-bonds. A remarkable feature of this structure is the nearly eclipsed conformation about the central C-CH3 bond. In the anhydrous crystal, both types of molecule have the normal staggered orientation of their Me groups. The reversal of the Me orientation in the trihydrate is attributed to C—H…O H-bonding, which must be much stronger and more directionally specific than has been previously assumed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720531
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Correct Structure of a Condensation Product C6H12N4O4 from Hydrazine, Formaldehyde and Hydrogen Peroxide (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2614-2616 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The compound mentioned in the title is shown by X-ray analysis to be 1, 2, 7, 8-tetraaza-4, 5, 10, 11-tetraoxatricyclo [6.4.1.12, 7] tetradecane, contrary to previous suggestions. The torsion angle about the peroxo bonds in the seven-membered rings in 100°, close to the value in hydrogen peroxide, which would not be possible in a six-membered ring.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640818
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    X-Ray Study of the Deformation Density in Tetrafluoroterephthalodinitrile: Weak Bonding Density in the C, F-BondA preliminary account of this work was presented at the 12th International Congress of Crystallography, Ottawa, Canada, 16-25 August 1981 [1]. (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 123-133 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A careful deformation density study of tetrafluoroterephthalodinitrile at 98K has been made from X-ray diffraction measurements. Prominent ‘bonding density’ peaks are found at or near the mid-points of the C, C- and C, N-bonds but not for the C, F-bonds, which show only weak density. Similarly weak bonding densities for C, F-bonds are also found for 1, 1, 4, 4-tetrafluorocyclohexane. The possible significance of these results in terms of bonding theory is briefly discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660113
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Crystal Structure of 1,1,4,4-Tetrafluorocyclohexane at 95 K (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 134-137 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of 1,1,4,4-tetrafluorocyclohexane has been determined from X-ray diffraction measurements at 95 K. Internal motion of the CF2-group can be discerned from analysis of the atomic vibration tensors. The pattern of bond lengths suggests that an anomeric-effect type of interaction between antiperiplanar C,C- and C,F-bonds (as well as between C,H- and C,F-bonds) may be operative in this molecule.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660114
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Crystal Structure and Electron-Density Distribution of Two [1.1.1] Propellane Derivatives at 81 K (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2100-2110 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structure and electron-density distribution of two [1.1.1]propellane derivatives have been determined from accurate single-crystal X-ray diffraction measurements at 81 K. The crystals of these highly reactive compounds (both are liquid at room temperature) were grown directly on the X-ray diffractometer at ca. 208 and 228 K, respectively. Both compounds crystallize in the space group P21/c with one molecule in the asymmetric unit. The symmetry of the propellane C-atom skeleton is close to D3h for both molecules. The distances between the two bridgehead C-atoms are 1.587 and 1.585 Å, and the mean lengths of the propellane side bonds are 1.525 and 1.528 Å, respectively. The deformation density peaks of the propellane side bonds (ca. 0.25 e/Å3) lie somewhat outside the internuclear connection lines and so correspond to ‘bent bonds’ as expected. On the other hand, the difference electron density between the bridgehead nuclei is slightly negative in both molecules. An interesting feature, observed in these difference maps, is presence of a diffuse, positive difference density at each inverted C-atom, outside the bridgehead bond, a probable site of electrophilic attack.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710827
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Structure and Reactivity of Five- and Six-Ring N, N-, N, O-, and O, O-acetals: A lesson in allylic 1, 3-strain (A1, 3 strain) (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 913-934 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray structures of fifteen 1, 3-imidazolidine, 1, 3-oxazolidine, 1, 3-dioxan-4-one, and hydropyrimidine-4(1H)-one derivatives are described (Table 2) and compared with known structures of similar compounds (Figs. 1-20). The differences between structures containing exocyclic N-acyl groups and those lacking this structural element arise from the A1,3 effect of the amide moieties. Even t-Bu groups are forced into axial positions of six-ring half-chair or into flag-pole positions of six-ring twist-boat conformers by this effect (Figs. 16-20). In the N-acylated five-membered heterocycles, a combination of ring strain and A1, 3 strain leads to strong pyramidalizations of the amide N-atoms (Table 1) such that the acyl groups wind up on one side and the other substituents on the opposite side of the rings (Figs. 4-9 and Scheme 3). Thus, the acyl (protecting!) groups strongly contribute to the steric bias between the two faces of the rings. Observed, at first glance surprizing stereoselectivities of reactions of these heterocycles (Schemes 1 and 2) are interpreted (Scheme 3) as an indirect consequence of the amide A1, 3 strain effect. The conclusions drawn are considered relvant for a better understanding of the ever increasing role which amide groups play in stereoselective syntheses.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750326
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Dendrophanes: Novel Steroid-Recognizing Dendritic Receptors. Preliminary Communication (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 779-788 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The H2O-soluble dendritic cyclophanes (dendrophanes) 3-5 of first to third generation with molecular weights up to nearly 20 kD were synthesized, purified, and characterized. Cyclophane 2, which served as the initiator core (generation zero), was prepared from tetrabromocyclophane 10 in a four-step sequence which involved as the first transformation a high-yielding, four-fold Pd(0)-catalyzed Suzuki cross-coupling reaction with 4-(benzyloxy)-phenyl-boronic acid to give 18. The X-ray crystal-structure analysis of tetrabromocyclophane 10 displayed an open, nearly rectangular box with opposite aromatic walls being 8.3 and 11.4 Å apart and of suitable size for the incorporation of steroidal substrates. 1H-NMR Binding titrations in borate-buffered D2O/CD3OD 1:1 showed that cyclophane-tetracarboxylate 2 forms 1:1 inclusion complexes with steroids (Table 2). Complexation was found to be enthalpically driven with higher binding affinities measured for the more apolar substrates. 1H-NMR Titrations in the same solvent also provided clear evidence for core-selective complexation of testosterone (21) by the dendrophanes 3 (1st), 4 (2nd), and 5 (3rd generation) carrying up to 108 carboxylate surface groups. The stability of the corresponding 1:1 complexes was hardly affected by the size of the dendritic shell, although some generation-dependent conformational changes in the receptor cavity seemed to take place. Remarkably, host-guest exchange kinetics in all recognition processes were fast on the 1H-NMR time scale.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790320
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    The X-Ray Crystal Structure and Packing of a Hexakis-adduct of C60: Temperature dependence of weak C—H…O interactions (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1047-1058 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure and packing of the C60 hexakis-adduct 1 has been determined from accurate X-ray diffraction measurements. The largest deformations on the C60 surface occur within the bridged pyracylene subunits; the bridgehead 6-6 bond lengths of the four cyclopropane and the two cyclohexene rings, attached in pseudo-octahedral positions, are close to 1.6 Å. Significant deformations also occur in the remaining part of the C60 skeleton, not bridged to any of the functional groups. The crystal packing, analyzed at 270, 230, and 180 K is characterized by a three-dimensional network of 14 weak C—H…O interactions. For most of these, H…O and C…O distances decrease on cooling the crystal specimen, indicating that they are attractive in nature. On the other hand, the shortest, nearly linear C(sp3)—H…O contact seems to be repulsive, since cooling of the crystal specimen leads to significantly longer H…O and C…O distances and to a reduction of the C—H…O linearity. Probably as a result of this intermolecular expansion, strain is produced in the crystal. Depending on the crystal-mounting procedure, this can lead either to a disordered structure (below ca. 200 K), or to destruction of the crystal specimen.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790413
    Library Location Call Number Volume/Issue/Year 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...