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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 58 (1993), S. 7084-7088 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1515-1519 
    ISSN: 0947-3440
    Keywords: Macrocycles ; Recognition ; Piperazines ; Self-assembly ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by H—C—H…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phane 8b (di-dihydrochloride salt) adopts a chair-chair conformation, confirming that protonation of the N atoms does not change the conformation.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1611-1615 
    ISSN: 0947-3440
    Keywords: Macrocycles ; Inclusion compounds ; Piperazines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New piperazine-based macrocycles with single small cavities were prepared by using high dilution technique. The inclusion of acetonitrile into the cavity (7, 8) or clathrate formation (3) was studied by 1H-NMR spectroscopy in solution and by X-ray diffraction in the crystalline state. The cycle 3 forms a molecular cleft, a molecular pocket, where the acetonitrile molecule is held by four weak N…H interactions reinforcing the clathrate formation. The cycles 7 and 8 contain a rigid cavity for an exact sterical fit with the methyl group of a linear compound like acetonitrile. The acetonitrile inclusion complex with 7 proved to be stable under normal conditions and was studied by means of thermogravimetry. It is stable up to 80°C and the breakdown is complete when the temperature is raised over 120°C. Solid-state IR studies show a shift of the cyano band of 5 cm-1 to smaller wave numbers when compared with free acetonitrile. The acetonitrile methyl group is shielded and in the 1H-NMR spectrum its signal is shifted to δ = 1.85.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: copper ; pseudorotaxanes ; self-assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1823-1832 
    ISSN: 0947-6539
    Keywords: calixarenes ; hydrogen bonds ; molecular boxes ; noncovalent assembly ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form well-defined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 10-4M. This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 1H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Furthermore, the synthesis of twelve new 1,3-bis(melamine)calix[4]arenes carrying different numbers and types of functionalities at the upper rim is described. Detailed 1H NMR spectroscopic studies on the assembly behavior of these functionalized calix[4]arenes shows that 1) polar substituents (e.g. nitro, cyano) hardly affect the stability of the hydrogen-bonded assembly; 2) hydrogen bond donating or accepting groups, like amino and acetamido, can disturb assembly of the boxes under certain conditions by destabilizing the calix[4]arene pinched cone conformation as a result of intramolecular hydrogen bond formation; and 3) sterically bulky groups (e.g. tBu) can significantly inhibit the formation of the hydrogen-bonded assembly, but this effect very much depends on the exact positions of the groups.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 649-656 
    ISSN: 0947-3440
    Keywords: Catenanes ; Interlocked rings ; Mechanical bond ; Photoswitches ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four catenanes (1-4) and the corresponding tetracationic monocycles 5-8 are synthesized. X-ray structural analyses allow a prediction of the mobility (circumrotation) of the „interlocked“ rings in the catenanes, which is proven by 1H-NMR spectroscopy. An unexpected order in the crystal packing of 6 is demonstrated. (E/Z) isomerization in one ring influences the second ring of 1-4 and inversely. An existing obstacle inside the cavity of the switchable macrocycle can block this isomerization completely.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1585-1595 
    ISSN: 0947-6539
    Keywords: concave hydrocarbons ; cyclophanes ; host/guest chemistry ; ion-selective electrodes ; prismands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concave hydrocarbons, such as 1 (C36H36), 4 (C60H60), 5 (C54H48), and 6 (C60H52), represent three-dimensionally clamped analogues of π-prismands. They encapsulate small metal ions and accomplish metal-ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion-selective electrodes. The synthetic route is based on well-established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 749-754 
    ISSN: 0947-6539
    Keywords: clathrates ; host-guest chemistry ; hydrogen bonds ; macrocyclic ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterisation of eleven new macrocyclic ethers (up to 96-membered [6+6] gigantocycle) with well-defined cavities are described. Syntheses of the macrocycles M1-M7 were performed under high-dilution conditions. A “supramolecular” purification method was used for the small [2+2] macrocycles M3-M7, which separated selectively from the reaction mixture on recrystallisation from a dichloromethane/diethyl ether solution mixture. This proved to be an excellent method for purifying [2+2] macrocyclic ethers containing 1,1-diphenylmethane moieties, and the separation was nearly quantitative. Molecular inclusion of dichloromethane in the cavities of noncovalently bonded macrocyclic ethers M2-M5 was studied by X-ray diffraction in the solid state. Additionally, clathrate formation was found for macrocycles M1 (including diethyl ether), M2 (including water), M6 (including benzene) and M7 (including benzene).
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 1434-1948
    Keywords: Schiff-bases ; Helical structures ; Structure elucidation ; NMR spectroscopy ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cadmium(II) complexes of two Schiff bases, 1,3-di(pyridine-2-carboxaldimino)propane (C15H16N4, L1)[1] and tris[4-(2′-pyridyl)-3-aza-3-butenyl]amine (C24H27N7, L2)[2] are described. An efficient route utilising molecular sieves for the synthesis of Schiff bases is presented. The ligands L1 and L2 can be described as linear and three-armed podands, respectively, L1 being conformationally flexible and L2 preorganised. Cadmium perchlorate in methanol with L1 yields a crystalline complex [Cd(L1)2](ClO4)2 (1), the structure of which was determined by X-ray structure analysis. The complex 1 has an unusual nonsymmetrical 8-coordinated helical structure and crystallizes in an acentric space group (Cc, no. 9) as a pure enantiomer due to spontaneous resolution. Solution studies of 1 in CHCl3/DMSO (10:1) and pure DMSO were performed using 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy and they suggest a reorientation of 1 into the more symmetrical 4-coordinate complex due to the flexible nature of L1. The preorganised, potentially tetra-, hexa- or heptadentate, three-armed podand L2 and its in situ complexation with the Cd2+ cation were investigated by 1H-, 13C-, 113Cd-NMR and 1H,15N z-GS HMBC spectroscopy. The results support the formation of a highly symmetrical helical 6-coordinate podate [CdL2](NO3)2 (2). The structure of 2 has also been verified by ab initio HF-MO calculations using a standard 3-21G* basis set (Lan2DZ for Cd).
    Type of Medium: Electronic Resource
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