Library

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
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Inorganic chemistry 34 (1995), S. 432-435 
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 12338-12339 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 5105-5113 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The complex between (R)-4,5,7,8,10,11,13,14,16,17-decahydro-2,19-diphenyldinaphtho[2,1-q:1′,2′-s][1,4,7,10,13,16]hexaoxa[2,5,8,11,14,17,19]cycloicosaheptene {Chemical Abstracts name: (R)-4,5,7,8,10,11,13,14,16,17-decahydro-2,19-diphenyldinaphtho[2,1-q:1′,2′-s][1,4,7,10,13,16]hexaoxacycloicosin} and D-2-phenylglycinium methyl ester perchlorate, C9H12NO_2^+.ClO_4^-.C42H40O6.H2O, crystallizes in the orthorhombic space group P212121 with two C9H12NO_2^+.C42H40O6 complexes, two ClO_4^- ions and two molecules of water in the asymmetric unit. Crystal data: Mr = 924.44, a = 23.048 (7), b = 34.383 (6), c = 11.992 (6) Å, V = 9503 (6) Å3, Z = 8, Dx = 1.292 Mg m−3, F(000) = 3904, μ(Cu Kα) = 1.261 mm−1, T = 175 K, R = 0.0896 for all 7784 reflections, 1208 parameters refined in three blocks with 29 restraints. Nearly twenty years elapsed between the first data collection and the solution of the structure with the direct-methods program CRUNCH. The structural details are of interest because enantiomers of this host show a high degree of discrimination between enantiomers of α-amino acids and their esters. The crystal structure demonstrates the influence of C—H...O and C—H...π interactions on the unexpected orientation of the guest in the host cavity. The same orientation is found in both of the unique complexes, and the geometric details are in agreement with solution studies.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexation of N-benzyloxycarbonyl (Cbz) derivatives of the excitatory amino acids L-aspartic acid (Asp; 1), L-glutamic acid (Glu; 3), and, for the first time, L-kainic acid ((2S,3S,3S)-2-carboxy-4-(1-methylethenyl)pyrrolidine-3-acetic acid; Kai; 5) was studied in CDCl3 with a diversity of chiral receptors consisting of a 1,1′-binaphthyl spacer with (carboxamido)pyridine (CONH(py)) functionality attached to the 6,6′-positions in the major groove. Receptors of type A possess two N-(pyridin-2-yl)carboxamide H-bonding sites (e.g. 7), whereas type B-receptors have two N-(pyridine-6,2-diyl)acetamide residues attached (e.g. 8 and 9). Complexes of excitatory amino-acid derivatives and other, achiral α,β-dicarboxylic acids with these receptors are primarily stabilized by two sets of C=O···H—N and O—H ··· N H-bonds. Optically active type-A receptors such as (R)- and (S)-7 showed a preference for the larger Glu derivative, whereas type-B receptors such as (R)- and (S)-8 and (R)- and (S)-9 formed more stable complexes with the smaller Cbz-Asp. To improve the poor enantioselectivity shown by 7-9, additional functionality was introduced at the 7,7′-positions of the 1,1′-binaphthyl spacer, and the nature of the H-bonding sites in the 6,6′-positions was varied. Screening the diversity of new racemic receptors for binding affinity, which had been shown in many examples by Cram to correlate with enantioselectivity, demonstrated that (+)-10 and (+)-11 formed the most stable complexes with dicarboxylic acids, and these receptors were synthesized in enantiomerically pure form. Both are type-B binders and contain additional PhCH2O (10) and MeO (11) groups in the 7,7′-positions. By 1H-NMR binding titrations, the complexation of (R)- and (S)- 10 and (R)- and (S)-11 with the excitatory amino-acid derivatives was studied in CDCl3, and association constants Ka between 103 and 2 · 105 l mol-1 were measured for the 1:1 host-guest complexes formed. Whereas both 10 and 11 formed stable complexes, enantioselective binding was limited to the PhCH2O-substituted receptor 10, with the (R)-enantiomer complexing Cbz-Asp by 0.7 kcal mol-1 more tightly than the (S)-enantiomer. The structures of the diastereoisomeric complexes were analyzed in detail by experimental methods (complexation-induced changes in 1H-NMR chemical shifts, 1H{1H} nuclear Overhauser effect (NOE) difference spectroscopy) and computer modeling. These studies established that an unusual variety of interesting aromatic interactions and secondary electrostatic interactions are responsible for both the high binding affinity (—ΔG° up to 7.2 kcal mol-1) and the enantioselection observed with (R)- and (S)-10. In an approach to enhance the enantioselectivity by reducing the conformational flexibility of the 1,1′-binaphthyl spacer, an additional crown-ether binding site was attached to the 2,2′-positions in the minor groove of the type-B receptors (R)- and (S)-48. Both the binding affinity and the enantioselectivity (Δ(ΔG°) up to 0.7 kcal mol-1) in the complexation of the excitatory amino-acid derivatives by (R)- and (S)-48 were not altered upon complexation of Hg(CN)2 at the crown-ether binding site, demonstrating lack of cooperativity between the minor- and major-groove recognition sites.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) 1 as well as of a great diversity of differentially mono-, di-, and triprotected derivatives by newly developed synthetic routes is described. These fully cross-conjugated molecules are versatile building blocks and precursors to two-dimensional all-C networks and novel C-rich nanoarchitecture with unusual structural and electronic properties, such as perethynylated expanded radialenes, or molecular wires and polymers with the novel polytriacetylene backbone. A key step in all of these routes was the Corey-Fuchs dibromoolefination of aldehydes and ketones. Dibromoolefination of silyl-protected penta-1,4-diyn-3-ones yielded the corresponding dibromomethylidene derivatives which, by twofold Pd-catalyzed alkyne coupling, were transformed into tetraethynylethene derivatives. In routes to tetraethynylethenes with free cis-or trans-enediyne moieties, dibromoolefination of aldehyde groups produced geminal dibromoethenes which, upon elimination/metallation with LDA followed by quenching with H+ or other electrophiles, yielded free or substituted ethynyl groups in high yields. Tetra- and triprotected tetraethynylethenes are rather stable compounds that could be isolated in pure form, whereas derivatives with two or more free ≡C—H termini were only stable in dilute solution and polymerized rapidly in pure form. A trans-bis(triisopropylsilyl)-protected derivative represented an exception and could be isolated as stable crystals. X-Ray analysis revealed that the two bulky (i-Pr)3Si groups isolate the reactive chromophores from one another in the crystal and prevent intermolecular reactions. The structures of several tetraethynylethenes were revealed in high-quality X-ray crystal structures.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Derivatives of fully cross-conjugated tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) 1 are versatile precursors to multinanometer-sized molecular rods with all-C-backbones. Oxidative polymerization (CuCl, N,N,N′,N′-tetramethylethylenthylenediamine (TMEDA), O2) of the trans-bis-deprotected trans-bis(triisopropylsilyl)-protected tetraethynylethene 2 yielded, after end-capping with phenylacetylene, the remarkably stable, soluble oligomers 3-7 with a persilylethynylated poly(triacetylene) (PTA) backbone [—(C≡C—CR=CR—C≡C)n—] and a length of 19.4 (3), 26.8 (4), 34.3 (5), 41.8 (6), and 49.2 (7) Å (Scheme 1). These compounds underwent facile one-electron reductions with the number of reversible reduction steps being equal to the number of tetraethynylethene moieties in each molecular rod. Oxidative Eglinton-Glaser homo-coupling of tetraethynylethenes 8-10 with a single free ethynyl group provided the fully silyl-protected 3,4,9,10-tetraethynyl-substituted dodeca-3,9-diene-1,5,7,11-tetraynes 11-13 (Scheme 2) and, after alkyne deprotection, the novel hydrocarbon 14, a C20H6 isomer, and its partially silyl-protected derivative 15. Oxidative hetero-coupling between two different tetraethynylethene derivatives, one with a single and the other with two free terminal ethynyl groups, yielded the extended chromophores 16-21 composed of 3 or 4 tetraethynylethene moieties (Scheme 3). The linearly conjugated oligomers 16 and 17 with the PTA backbone are isomeric to 19 and 20, respectively, which are members of the cross-conjugated expanded dendralenes, i.e., dendralenes with butadiynediyl fragments inserted between each pair of double bonds [—(C≡C—C(=CR2)—C≡C)n—]. The electronic absorption spectra of these compounds were compared and analyzed in terms of the competition between linear and cross-conjugation in determining the extent of π-electron delocalization. Although steric factors on π-electron conjugation remain to be clarified, this analysis strongly suggests that cross-conjugation is not an efficient mechanism for π-electron delocalization. All extended acetylenic-olefinic chromophores considered in this study exhibited remarkably high stability and did not decompose when exposed to laboratory air and light for months. In agreement with this observation, electrochemical studies demonstrated that the compounds are difficult to oxidize with the oxidation potentials in THF (0.1M(Bu4N)PF6) being higher than 1.0 V (vs. the ferrocene/ferrocenium couple).
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) molecular scaffolding provided access to novel macrocyclic nanometer-sized C-rich molecules with unusual structural and electronic properties. Starting from cis-bis-deprotected cis-bis(trialkylsilyl)protected tetraethynylethenes, the per(silylethynyl)ated octadehydro[12]annulenes 1 and 2 and the corresponding dodecadehydro[18]annulenes 4 and 5 were prepared by oxidative Hay coupling. X-Ray crystal-structure analyses of (i-Pr)3Si-protected 2 and Me3Si-protected 4 showed that both annulene perimeters are perfectly planar. Electronic absorption spectral comparisons provided strong evidence that the macro rings in the deep-purple-colored 1 and 2 are antiaromatic (4n π-electrons), whereas those in yellow 4 and 5 are aromatic ((4n + 2) π-electrons). Although unstable in solution, the antiaromatic compound 2 gave high-melting crystals in which the individual octadehydro[12]annulene chromophores are isolated and stabilized in a matrix-type environment formed by the bulky (i-Pr)3Si groups. Electrochemical studies demonstrated that the antiaromatic octadehydro[12]annulene 2 undergoes two stepwise one-electron reductions more readily that the aromatic chromophore 5. This redox behavior is best explained by the formation of an aromatic (4n + 2) π-electron dianion from 2, whereas 5 loses its aromaticity upon reduction. The Me3Si derivative 4 was deprotected with borax in MeOH/THF to give the highly unstable hexaethynyl-dodecadehydro[18]annulene 6, a C30H6 isomer and macrocyclic precursor to a two-dimensional all-C-network. Deprotection of 2 did not give isolable amounts of tetraethynyl-octadehydro[12]annulene 3 due to the extreme instability of the latter. Starting from dimeric and trimeric acyclic tetraethynylethene oligomers, a series of expanded radialenes were obtained. They possess large C-cores with silylethynyl-protected peripheral valences and can be viewed as persilylated C40 (7), C50 (8), and C60 (9) isomers. These expanded C-sheets are high-melting, highly stable, soluble materials which were readily characterized by laser-desorption time-of-flight (LD-TOF) mass spectrometry. Due to inefficient macrocyclic cross-conjugation and/or non-planarity, the extent of π-electron delocalization in 7-9 is limited to the longest linearly conjugated π-electron fragment. In agreement with these properties, all three expanded radialenes exhibited similar redox behavior; they are difficult to oxidize but undergo several reversible one-electron reductions in similar potential ranges. Presumably, the reduced π-electron delocalization is also at the origin of the particularly high stability of 7-9.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...