Library

Your email was sent successfully. Check your inbox.

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

Proceed reservation?

Export
Filter
  • 1995-1999  (1,656)
  • 1995  (1,656)
  • General Chemistry  (1,656)
  • Nuclear reactions
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    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
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    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
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 3-3 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    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
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 7-11 
    ISSN: 0947-6539
    Keywords: density-functional calculations ; ion-molecule reactions ; relativistic effects ; thermochemistry ; uranium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nitridooxouranium cation NUO+ has been prepared as a new isoelectronic homologue to the uranyl dication UO22+ by a sequence of ionmolecule reactions starting from the atomic uranium cation U+. Collision-induced dissociation experiments and ligand-exchange reactions serve to unambiguously identify the ion as a species in which the uranium cation is formally inserted in the NO molecule. New thermochemical data for NUO+ and UN+ are given, and the stability of NUO+ with respect to UO22+ is investigated by means of quasi-relativistic density-functional calculations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 0947-6539
    Keywords: asymmetric catalysis ; aziridines ; chiral ligands ; palladium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral palladium π-allyl intermediate for the catalytic asymmetric synthesis shown in Scheme 1 has been isolated as the PF-6 salt. MM 2 calculations have been performed and the structure of the palladium complex in solution has also been investigated by means of NMR spectroscopy. Both the computational and spectroscopic results suggest that in the complex the bidentate bis(aziridine) ligand adopts a conformation that forces the π-allyl moiety out of the normally preferred square-planar geometry. This nicely explains the very high enantioselectivity observed in the title reaction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 0947-6539
    Keywords: chlorine complexes ; ethene complexes ; intermediates ; rotational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π-donor-acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π-bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub-nosed”.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 0947-6539
    Keywords: alkoxides ; clusters ; Group 15 complexes ; Lewis acids ; oxygen bridges ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As(OtBu)3 does not form adducts with alkali metal tert-butoxides MOtBu (M = Li, Na, K, Rb and Cs), whereas the corresponding Sb(OtBu)3 (2) and Bi(OtBu)3 (3) react with MOtBu (M = K, Rb, Cs) to yield M(OtBu)4Sb (M = K (6), Rb (7), Cs (8)) and M(O-tBu)4Bi (M = 9), respectively. X-ray structure determinations for 6 and 9 show them to be one-dimensional coordination polymers composed of E(OtBu)4 (E = Sb, Bi) units linked through potassium atoms. These E(OtBu)4 units display a ψ-trigonal-bipyramidal coordination around the metal atom (Sb—O = 1.971(2) and 2.181(2) Å, Bi—O = 2.068(8) and 2.275(8) Å). Both the structures exhibit a planar four-coordinate environment of oxygen around the potassium atoms (K—O = 2.650(2)-2.967(2) Å in 6, 2.53(1)-3.15(1) Å in 9). Compound 2 reacts with two equivalents of KOtBu to afford K2Sb(OtBu)5 · dioxane (10), which contains Sb2K2O5 cage units and can be described as an O5 trigonal bipyramid with metal atoms inserted in the equatorial edges. Each metal atom is tetracoordinated by oxygen atoms of the cage (Sb—O = 1.979(3)-2.144(3) Å. K—O = 2.592(3)-2.778(2) Å). The dioxane molecules increase the coordination number at each potassium atom to five by forming bridges between the molecules through K—O bonds. Reaction of 2 and 3 with NaOtBu produce the cluster compounds Na4Sb2O(OtBu)8 (4) and Na4Bi2O-(OtBu)8 (5) in high yields. K4Sb2O-(OtBu)8 (11) is obtained in almost quantitative yield by heating KSb(OtBu)4 in benzene for 24 h. Compounds 4, 5 and 11 crystallise in rhombohedral lattices; the crystal structure analyses show a superposition of molecules. With an isotropic oxygen-centred M6 octahedron. The formation of these oxo-tert-butoxides is accompanied by evolution of isobutene. Addition of four equivalents of THF to 11 gives K4Sb2O(OtBu)8 · 4 THF (12). X-ray diffraction studies reveal a cis arrangement of the Sb atoms in the central OSb2K4 unit. K4Sb2O2(OiPr)12 (13) is obtained as the major product on heating KSb(OtBu)4 and subsequent reaction with isopropyl alcohol. In the crystal structure, two oxygen-centred Sb2K2 tetrahedra (K—O 2.693(4) Å, Sb—O = 1.982(5) Å) linked through iPrO—K bonds (2.726(7)-2.738(7) Å) are observed. In the reactions of KSb(OtBu)4 (6) with the metal halides CaCl2, TlCl and CuI, a halide ion is transferred to potassium; this results in formation of potassium halide, the corresponding alkoxide and Sb(OtBu)3.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 56-67 
    ISSN: 0947-6539
    Keywords: amethyrin ; orangarin ; porphyrinoids ; terpyrroles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, general synthesis of the first β-substituted tetra- and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(II)-mediated oxidative coupling of the LDA-derived enolates of α-keto pyrroles. The first new expanded porphyrin reported here, the so-called “orangarin”, contains five pyrrolic subunits and two bridging carbon atoms, and is formally a 20π-electron nonaromatic macrocycle. The second new class of expanded porphyrins, the “amethyrins”, are 24π-electron nonaromatic macrocycles containing six pyrrole units. Both of these new macrocycles, as well as one of the new terpyrrolic precursors have been structurally characterized by single crystal X-ray diffraction analysis.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 68-73 
    ISSN: 0947-6539
    Keywords: porphyrinoids ; Rothemund synthesis ; sapphyrin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Rothemund-type condensation of pyrrole and benzaldehyde yields, apart from 5,10,15,20-tetraphenylporphyrin (TPPH2) and inverted tetraphenylporphyrin 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (CTPPH2), a unique pentapyrrolic macrocyclic molecule with the aromatic nucleus of sapphyrin, namely, 5,10,15,20-tetraphenylsapphyrin (TPSH3). Its unorthodox structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrole unit accounts for the spectroscopic properties of the novel sapphyrin. The diprotonation of TPSH3 acts as a trigger for a structural transformation involving a flip of the pyrrole units, which relocates the 27-NH pyrrolic nitrogen from the periphery into the center of the macrocycle. The formation of 5,10,15,20-tetraphenylsapphyrin proves that the pentapyrrolic product is accessible by the mechanism of the Rothemund synthesis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 11
    ISSN: 0947-6539
    Keywords: catenanes ; cyclodextrins ; macrocycles ; orientational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel synthetic approach is described for the construction of catenanes in aqueous solution from a partially methylated cyclodextrin (CD)-namely, heptakis(2,6-di-O-methyl-β-cyclodextrin) (DM-β-CD)-and a range of substrate molecules that contain a hydrophobic central core in the form of a 4,4′-disubstituted biphenyl unit (usually bitolyl) carrying two hydrophilic polyether side chains terminated by primary amine functions. In water, the amphiphilic catenane precursors form 1:1 complexes with β-CD and DM-β-CD and 2:1 (guest: host) complexes with the larger γ-CD. Macrocyclizations of the biphenyl-containing substrates with aromatic diacid chlorides in aqueous solution and in the presence of DM-β-CD under Schotten-Baumann conditions afforded-in low yields-a range of [2]- and [3]catenanes. When a consitutionally asymmetrical diamine was employed as the substrate, orientational isomers of a [2]catenane were obtained. A [3]catenene incorporating a macrocyclic tetralactam was found to exist as a mixture of head-to-head and head-to-tail isomers, which could be separated by high pressure liquid chromatography and identified unambiguously by nuclear magnetic resonance spectroscopy. One of the [2]catenanes afforded good single crystals from which the solid state structure was determined by X-ray crystallography. Other techniques which aided the characterization of these novel compounds included ultraviolet/visible and luminescence spectroscopy, dynamic nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry. Generally speaking, the catenated cyclodextrins are soluble in halogenated and aromatic hydrocarbons as well as in hydroxylic solvents. The existence of these new compounds gives us a unique insight into the nature of the noncovalent bonding interactions that cyclodextrins employ in binding substrate molecules.
    Additional Material: 29 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 100-100 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 13
    ISSN: 0947-6539
    Keywords: chiral phenols ; facial selectivity ; photooxidations ; quinols ; singlet oxygen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three of the four possible isomeric para-substituted hydroxyethyl-methylphenols were prepared from readily available starting materials and submitted to photooxygenation. In the case of 3-hydroxy-α,6-dimethylbenzenemethanol (1 a) and 2-hydroxy-α,5-dimethylbenzene-methanol (1 b) the corresponding 4-hydroperoxy-3,5-cyclohexadienones were obtained as oxy-functionalized products (≥90%, d.r. 85:15 and 75:15). The stereochemistry of the products was assigned after reduction to the corresponding p-quinols. The ready cleavage of the initial oxygenated product, which can be observed at low temperature as a single diastereomer, prevented rigorous assignment of the π-facial selectivity of the singlet oxygen attack for the derivative 4-hydroxy-α,2-dimethylbenzenemethanol (1 c). The present stereochemical results indicate that the hydroxyl group directing effect, that is, coordination of the incoming singlet oxygen dienophile with the hydroxyl group, is also operating in the photooxygenation of the chiral phenols 1 a-c. However, in the case of the derivative 1 b, hydrogen bonding in the starting material leads to an opposite stereochemical outcome. This conclusion is further substantiated by solvent effects and the fact that the methyl ether 1 d of alcohol 1 c displays a significant lower diastereoselectivity.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 14
    ISSN: 0947-6539
    Keywords: chelate ligands ; hydrogen bonds ; ligand design ; mass spectrometry ; stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of compounds containing the mononuclear complexes [M(tdci)2]3+ (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol, M = Al, Fe, Ga, In) and [M(tdci)2]4+ (M = Ti, Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X-ray analysis of the AlIII, FeIII, GaIII, and InIII complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated oxygen donors and the six N—H protons form a hydrophilic pocket, whereas the two cyclohexane rings and the twelve methyl groups form two hydrophobic shells. The hydrophilic pocket is filled with twelve water molecules, which are arranged as a second and a third coordination sphere around the metal cation. The reactivity in aqueous solution was investigated by potentiometric measurements. The bis complexes proved to be stable at pH 7. The evaluated formation constants show an increase of stability in the order AlIII〈InIII〈GaIII〈FeIII. The measurements established that tdci is one of the most effective tridentate ligands for small (r ≤ 0.8Å) and highly charged cations. The different chelating properties of tdci and of the unmethylated 1,3,5-triamino- 1,3,5-trideoxy-cis-inositol are discussed in terms of different steric requirements and different types of solvation of the corresponding complexes in aqueous solution.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 15
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 111-117 
    ISSN: 0947-6539
    Keywords: alkyne complexes ; carbon networks ; macrocycles ; platinum compounds ; tetraethynylethene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the first organometallic mono- and dinuclear platinum complexes bearing the tetraethynylethene unit as an η1-ligand are reported. Structural characterization of two of the trans σ-bis(acetylide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic π-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments attached to one set of geminal acetylenes of tetraethynylethene was also investigated by X-ray diffraction. Hay coupling of a mononuclear species leads to the incorporation of the σ-bis(acetylide) moiety into a diplatinated metallacycle. This macrocyclic compound represents a novel structural motif in the design of a transition metal linked carbon network based on tetraethynylethene.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 118-123 
    ISSN: 0947-6539
    Keywords: antiferromagnetic exchange ; crystal structure ; indium compounds ; Jahn-Teller distortion ; titanium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dark green crystals of In3Ti2Br9 have been synthesized from elemental Ti and molten InBr3 at 450°C. The X-ray diffractional characterization by means of single-crystal and powder Rietveld refinement reveals a hexagonal crystal structure (a = 738.2(2), c = 1813.9(3) pm; P63/mmc, Z = 2) of Cs3Cr2Cl9 type, containing Ti2Br3-9 dimers and univalent indium cations. Self-consistent, semiempirical band structure calculations show the structural distortions of the two monovalent indium cations to arise from a second-order Jahn-Teller instability. The new compound's magnetic susceptibility and microscopic antiferromagnetic exchange are analyzed by using a Bleaney-Bowers ansatz.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 21
    ISSN: 0947-6539
    Keywords: calixarenes ; cavitands ; molecular modeling ; resorcinarenes ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coupling reactions of calix[4]arenes and modified resorcin[4]arenes have been investigated. Reaction of mono(chloroacetamido)calix[4]arene 4 with tetrahydroxycavitand 9 gave the 1:1 coupled product 13 in 61% yield. Combination of upper-rim 1,3-difunctionalized calix[4]arene 5 with 9 afforded predominantly the 2:1 calix-resorcinarene 18 in 47% yield. Reaction of 1,2-difunctionalized calix[4]arene 6 with 9 gave five products, namely, endo 1:1 (19), exo 1:1 (20), endo-endo 2:1 (21), endo-exo 2:1 (22), and exo-exo 2:1 (23) in ratios that depend on the reaction conditions. The stereochemistry of the different products was determined with NOESY experiments. The structures of 21 a and 23 b were calculated by using molecular mechanics, which revealed that intramolecular hydrogen bonds are only present in the former. Reaction of 1,2-bis(chloroacetamido)calix[4]arene 26, which has two additional nitro groups at the remaining aromatic rings, with 9 yielded three different products, namely, endo 1:1 (28), endo-endo 2:1 (30), and endo-exo 2:1 (32) in ratios that depend on the reaction conditions. There is a preference for the endo orientation in the formation of the 1:1 coupled product, probably owing to an interaction of the nitro groups with the cavitand in the transition state. After conversion of the nitro groups in 28 into chloroacetamido moieties, reaction with Cs2CO3 in DMF under high-dilution conditions afforded holand 33 in 26% yield together with calix[4]arene-based carceplex 34 with an encapsulated DMF molecule (27% yield). Holand 33 was obtained in 33% yield by reaction of the tetrakis(chloroacetamide) endo-endo 2:1 isomer 31 with tetrahydroxycavitand 9. Holand 33 contains a cavity of nanosize dimensions. Molecular mechanics simulations indicate that holand 33 adopts a conformation with eight hydrogen bonds and a large, preorganized cavity with two entrances of smaller dimensions. Molecular dynamics simulations of holand 33 in both CHCl3 and THF showed that four solvent molecules can be accommodated in the cavity at well-defined positions.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 22
    ISSN: 0947-6539
    Keywords: alkynes ; coupling reactions ; cyclopropanes ; macrocycles ; oligoalkadiynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general approach to the family of completely spirocyclopropanated macrocyclic polydiacetylenes, that is, cyclic dehydrooligomers of 1,1-diethynylcyclopropane 4, is reported. The characterized examples of these “exploding” [n]rotanes are for n = 5, 6, 7, 8, 9, 10, and 12. X-ray crystal structure analyses for the hydrocarbons with n = 5, 6, 7, and 8 disclose a strong electronic interaction between the cyclopropane and the acetylene units leading to a significant shortening of the distal and lengthening of the proximal cyclopropane bonds. While the five-sided compound 18 can occur as a planar or envelope-shaped molecule, depending on the solvent from which crystals are grown, the six- (19), seven- (20), and eight-sided (21) molecules all have chair conformations. While the butadiyne units in 18 and 19 are bent slightly outwards, those in the seven- and eight-sided molecules 20 and 21, respectively, are bent distinctly inward. All these compounds are extremely high-energy molecules: when struck with a spatula or a pestle, they go off with a puff to yield black soot.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 23
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 261-265 
    ISSN: 0947-6539
    Keywords: crystal structure ; fluorides ; hexafluorobromate(V) ; hexafluoroselenate(IV) ; naked fluoride ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,1,3,3,5,5-Hexamethylpiperidinium fluoride (pip+F-) and 1,2-dimethylpropyltrimethylammonium fluoride have been prepared. They dissolve in fluorohydrocarbons (CH2F2, CF3-CHF-CF3, CHF3) even at very low temperatures. The nature of these solutions is indicated by the crystal structure of the adduct pip+F-·4CH2F2, which shows (C)H…F bridging. The high fluoride activity is exemplified by the previously unknown reaction between SeF5- and F- to yield SeF62-. The salt pip+BrF6- is obtained by a metathesis reaction of Cs+BrF6- with pip+F-. The distortion of the SeF62- structure from octahedral symmetry is intermediate between IF6- (strongly distorted) and BrF6- (octahedral). The electron-pair repulsion model is checked against these results.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 25
    ISSN: 0947-6539
    Keywords: amphiphiles ; C-glycosides ; cryptates ; fullerenes ; ionophores ; Langmuir-Blodgett films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air-water interface were investigated in a systematic study. Among these derivatives are Diels-Alder adducts of C60 and methanofullerenes, four of which are fullerene C-glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and optical light microscopy. UV/Vis spectroscopy and small-angle X-ray diffraction (SAXS) were employed for LB film characterization on solid substrates. Parameters influencing the spreading and monolayer character include (a) polarity, (b) balance of hydrophobicity to hydrophilicity, (c) size and bulkiness of the polar groups attached to the fullerene, and (d) presence of aromatic residues in these groups.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 26
    ISSN: 0947-6539
    Keywords: benzene ; benzyne ; osmium clusters ; photochemistry ; polymer films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The highly efficient photoinduced isomerisation of [Os3(CO)9(μ3-η2:η2:η2-C6H6)] (1) to the previously characterised μ3-benzyne complex [H2Os3(CO)9(μ3-η2:η1:η1-C6H4)] (2) is described. We find that for the more electron-rich clusters [Os3(CO)9-n(PPh3)n(μ3-η2:η2:η2-C6H6)] (n = 1 or 2) the efficiency of the photolytic process is improved. We suggest that photolysis generates a vacant site at osmium (mimicking the inherent coordinative unsaturation of a metal complex) and that this transformation offers a compelling model for the interconversion of associatively and dissociatively chemisorbed benzene. Moreover, we can fine-tune our molecular “work function” (really the separation of HOMO/LUMO energies) by protonation or by phosphine substitution for CO at the metal. Thus, the cation [HOs3(CO)9(μ3-η2:η2:η2-C6H6)]+ does not undergo internal metalation, while photoisomerisation of the electron-rich phosphine derivatives proceeds more readily than for 1. We find that these photolytic reactions are easily monitored by IR spectroscopy for samples suspended in polymethylmethacrylate films under ambient conditions. This method permits “matrix isolation” experiments under ideal conditions. Finally, we speculate that the mechanism of interconversion almost certainly involves the symmetric cleavage of a Os—Os bond (σ-σ* transition) to produce an extremely reactive diradical intermediate.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 29
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 436-440 
    ISSN: 0947-6539
    Keywords: ab initio calculations ; copper compounds ; organometallic compounds ; tetrahydroborato ligand ; theoretical chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All-electron ab initio calculations (MP4/MP2 level) have been performed on [Cu(BH4)(PH3)n] (n = 1, 2, 3) complexes. Full-geometry optimizations were carried out in each case, and the stationary points were characterized by the diagonalization of the analytically calculated Hessian matrix. The η2 coordination mode, with a tetrahedral arrangement around the copper atom, is the most stable structure for n = 2, while for n = 3 a strongly nonlinear η1 coordination mode is preferred. These results are in agreement with the experimental data available on related complexes. For n = 1, for which there is no experimental data, the η3 structure turns out to be the most stable. The energy differences associated with some changes in the coordination mode (η1 → η2 for n = 3 and η3 → η2 for n = 1) are small. Finally, a mechanism for the exchange between terminal and bridging hydrogen atoms is proposed for each complex under study.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 30
    ISSN: 0947-6539
    Keywords: chelate ligands ; coordination ; hydrogen bonds ; ligand fields ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1- and 2-D coordination polymers [Mn{HB(C2H2N3)3}2(H2O)2].4H2O (11) and [Ni{H2B(CHN4)2}2-(NH3)2] (13), respectively, and the chelate complex [Ni{H2B(C2H2N3)2}2(H2O)2] · 2H2O (12) were synthesized and structurally characterized. The compounds contain ambidentate poly(azolyl)borato ligands (azolyl = triazolyl or tetrazolyl), which can chelate or bridge metal centers. The metal-ligand structures in 11-13 differ from the known coordination modes of the poly(azolyl)borates towards other metal centers. We describe how a change in the metal and/or the conditions of crystallization affects the ligand-field stabilization energy and favors one type of nitrogen donor atom over the other for the poly(triazolyl)borato ligands. The crystal structures of 11 and 12 contain additional water of crystallization; this leads to hydrogen-bonded solvent substructures. In the case of the bis(triazolyl)borato ligands. The crystal structures of 11 and 12 contain additional water of crystallization; this leads to hydrogen-bonded solvent substructures. In the case of the bis(tetrazolyl)borato ligand the water substructure is shown to function as a “reinforcing bar” that symmetrizes the metal-ligand grid sheet.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 31
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 183-192 
    ISSN: 0947-6539
    Keywords: adenine ; catalysis ; molecular recognition ; template effects ; transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of receptors were prepared all containing two adenine binding sites linked by various spacers. Their ability to act as templates in the coupling of two adenine derivatives, an active ester and an amine, in CHCl3 was evaluated. The accelerations varied from none to 700-fold. Binding studies of the coupling product with these templates confirmed involvement of both binding sites. When the spacer was a 1,10-phenanthroline unit, an efficient hydrolysis reaction of the active ester was observed. Another series of receptors were prepared containing one adenine receptor and various polar functional groups. The molecules were evaluated as catalysts in the coupling of an adenine-derived active ester and n-butyl-amine. The orientation as well as the nature of the functional group greatly influenced the coupling rate. A carboxylate group was most effective, accelerating the intracomplex reaction 250-fold.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 35
    ISSN: 0947-6539
    Keywords: chiral mesophases ; Langmuir-Blodgett films ; liquid crystals ; phthalocyanines ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and physical properties of optically active, metal-free 2,3,9,10,16,17,23,24-octa (S-3,7-dimethyloctoxy)phthalocyanine ((S)-Pc(8,2)) are reported and compared with those of the phthalocyanine with (R,S) side chains (mixture of 43 stereoisomers). Unlike the latter compound, (S)-Pc(8,2) lacks a crystalline phase. A freshly prepared sample is in a distorted mesophase and reorganizes irreversibly to a more ordered phase above 65 °C. X-ray diffraction and circular dichroism studies indicate that the molecules are stacked in columns which have a hexagonal arrangement and a left-handed helical superstructure, that is, a novel chiral Dh* mesophase. Solid state NMR measurements reveal that the phthalocyanine units in the columns begin to vibrate laterally when the temperature is increased. At 111 °C (Dh* → Dr transition) they start to rotate around their columnar axes and at the same time the side chains become liquidlike. Energy migration is very efficient in the chiral Dh* phase and also in the frozen mesophase below 3 °C, as follows from luminescence spectroscopy. Intracolumnar charge transport, studied by the time-resolved microwave conductivity technique, turns out to be slower in the helically distorted columns than in linear columns. (S)-Pc(8,2) forms a very stable bilayer at the air-water interface, which can be transferred to give a high quality Langmuir-Blodgett film. The fact that this phthalocyanine is mesogenic at room temperature is thought to be responsible for this behavior.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 36
    ISSN: 0947-6539
    Keywords: ab initio calculations ; Claus process ; elemental sulfur ; sulfane oxides ; sulfur oxoacids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-level ab initio MO calculations (MP2/6-311G**//MP2/6-311G**) on 16 isomeric forms of H2S3O (including rotamers) have been performed. The nonhelical hydroxotrisulfane HOSSSH 1a (motif + + -) is the most stable isomer, while the chains with motifs + + + and + - + are less stable by 1.7 and 3.7 kJ mol-1, respectively. The other isomers of H2S3O increase in energy in the order HSS(O)SH 〈 HOS(S)SH 〈 HSOSSH 〈 HS(O)SSH 〈 HS(S)SOH 〈 HS(S)OSH. The trisulfane-2-oxide HSS(O)SH 2a (symmetry C1) is less stable than 1 a by 67 kJ mol-1. These molecules may be formed from H2S and SO2 via H2S2O2 by condensation with H2S. The calculated reaction energies support the view that H2S3O is a key intermediate in the room-temperature reaction of H2S and SO2 resulting in the formation of lower oxoacids of sulfur and finally in sulfane oxides.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 199-203 
    ISSN: 0947-6539
    Keywords: benzyl ligands ; catalysis ; chromium compounds ; ferromagnetic coupling ; polymerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of [{Cp*Cr(μ-Cl)}2] with benzyllithium yielded [{Cp*Cr-(μ-Bz)}2] (1), a CrII alkyl complex with bridging benzyl groups and a Cr—Cr bond, which rearranged at room temperature to [Cp*Cr(η1-Bz)(μ-η3:η6-Bz)CrCp*] (2), a mixed valent (CrI/CrIII) complex with a benzyl ligand coordinating as an η6-arene ligand to one chromium and as an η3-allyl ligand to the other one. Upon heating, 2 reductively eliminated bibenzyl and yielded [(Cp*Cr)2(μ-η6:η6-Bz-Bz)] (3), in which two 17-electron sandwich complexes are linked by an ethano bridge. The crystal structures of 2 and 3 have been determined. Magnetic susceptibility and saturation magnetization measurements showed 2 to be ferromagnetically coupled (ground state S = 2, J = + 23(1) cm-1). Of the three isomers, only 2 catalyzed the polymerization of ethylene, presumably because it contains a CrIII alkyl.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 39
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 40
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 41
    ISSN: 0947-6539
    Keywords: dendrimers ; luminescence ; molecular devices ; ruthenium complexes ; redox systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treelike (dendritic) structures made of RuII-polypyridine complexes have been prepared by the “complexes-as-metals and complexes-as-ligands” synthetic strategy. The key building blocks are RuII complexes of the 2,3-bis-(2-pyridyl)pyrazine(2,3-dpp) bridging ligand, where one of the two chelating sites can be protected by methylation. Dendrimers containing four, ten, and twenty-two metal ions have been obtained. These dendrimers exhibit strong absorption in the UV/Vis spectral region, a moderately strong red luminescence, and a great number of metal-based oxidation and ligand-based reduction processes. The nature of the terminal ligands determines in which subunits of the supramolecular array the HOMO and LUMO orbitals and the luminescent excited state are localized. The reported synthetic strategy is efficient, characterized by a full, step-by-step control of the growth process, and can be easily extended to building blocks containing other metals and/or ligands.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 42
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 232-235 
    ISSN: 0947-6539
    Keywords: carbonyl complexes ; cobalt compounds ; kinetics ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The substitution reaction of [Co(CO)4]- by P(OPh)3 was investigated in THF. Under a CO atmosphere, the reaction consists of an equilibrium, which, in order to be established, needs [Co2(CO)6(P(OPh)3)2]. The catalysis by this neutral carbonyl is formally related to a previously reported case, where either [Co2(CO)8] or [Co4(CO)12] was found to be necessary for the 13CO scrambling in [Co(CO)4]-. The kinetic analysis reported in this paper indicates, however, that the two CO labilizations differ in their mechanism-the substitution by P(OPh)3 is ascribed to a disproportionation-synproportionation of [Co2(CO)6(P(OPh)3)2].
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 43
    ISSN: 0947-6539
    Keywords: electronic structure ; frontier orbitals ; metalloporphyrins ; radical cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of magnesium and zinc tetraarylporphyrins and their porphyrinoxidized derivatives were studied by UV/Vis, ESR, and resonance Raman spectroscopy at various temperatures. The series included tetra(meta-dichlorophenyl)porphyrinatozinc (5), tetra(ortho-dichlorophenyl)porphyrinatozinc (6), tetra(ortho-difluorophenyl)porphyrinatozinc and -magnesium (9 and 10), and tetra(pentafluorophenyl)porphyrinatozinc and -magnesium (7 and 8). The radical cations (3a-10a) were isolated by chemical one-electron oxidation of their neutral precursors (3-10). Despite the structural similarity of all these radicals, their electronic ground state varied within the series. The position of the chloro groups was found to play a key role. While the radical cation of the meta-dichloro-substituted derivative 5a exhibited A2u spectroscopic features, the ortho-dichlorophenyl derivative (6a) showed A1u spectral features. Radicals of the fluoro-substituted porphyrins, especially that of 10, were found to have state-admixed (A1u/A2u) electronic structures, and the relative contributions of the two states was found to vary with temperature and to depend on the axial ligand. The results indicate that the fluoro-substituted porphyrins are primarily A2u at low temperature, even though their room temperature spectroscopic features resemble those of A1u cations. The elucidation of factors that affect the electronic structures of the radicals in the present series is helpful in providing a greater understanding of the spin-spin interactions in the intermediates of heme-dependant enzymatic reactions and their synthetic analogues.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 44
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; enol ethers ; Fischer carbenes ; Michael additions ; syn diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Michael addition reactions of ketone and ester lithium enolates to optically active Fischer vinylcarbene complexes derived from (-)-8-phenylmenthol take place with high syn selectivity and high levels of asymmetric induction. The initial Michael adducts can be further elaborated through diastereoselective addition of organometallic reagents to ketones and aldol reactions. Removal of the metal fragment and chiral auxiliary group leads to cyclic enol ethers with three or five contiguous stereogenic centers and of high enantiomeric purity.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 45
    ISSN: 0947-6539
    Keywords: crystal structure ; polynuclear ; complexes ; ruthenium compounds ; supramolecular chemistry ; terpyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bridging ligand bis{4′-(2,2′:6′,2″-terpyridinyl)}ether (1) can be prepared in 69% yield from the reaction of 4′-chloro-2,2′:6′,2″-terpyridine (3) with 2,2′:6′,2″-terpyridin-4′(1′H)-one (2) in Me2NCHO in the presence of KOH. More conveniently, complexes of 1 can be prepared in situ by the reaction of 2 with a ruthenium(II) complex of 3 in the presence of K2CO3. This methodology has been developed for the synthesis of a range of mono-, di-, tri- and hexanuclear complexes with a variety of Xtpy (Xtpy = 4′-substituted 2,2′:6′,2″-terpyridine) terminator ligands. The molecular structure of 1 (a = 9.623(2), b = 11.241(1), c = 11.828(1) Å; space group P1; α = 93.064(9), β = 107.072(14), γ = 99.088(14)°; Z = 2, R = 0.0450, Rw = 0.0577) has been determined. The generality of the methodology may ultimately be limited by the sensitivity of the ether-linkage in 1 to attack by nucleophiles.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 46
    ISSN: 0947-6539
    Keywords: allylic substrates ; carbon-carbon coupling ; catalysis ; copper compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regioselectivity in the arenethiolatocopper(I)-catalyzed crosscoupling reaction of allylic substrates was studied. It was found that allylic acetates gave highly γ-selective reactions in Et2O at 0°C with slow addition of the Grignard reagent, whereas α-selective reactions were obtained in THF at -30°C with fast addition of the Grignard reagent. It is proposed that the formation of an intermediate in Et2O, in which the allylic acetate coordinates in a bidentate fashion the arenethiolatocopper(I) catalyst, dramatically increases the reactivity of the leaving group and results in excellent γ-selectivity. The remarkable observation that an allylic acetate can be made more reactive than an allylic chloride by using the arenethiolatocopper(I) catalyst 1a supports the theory of a bidentate coordination of the substrate to the catalyst through its double bond and acetate oxygen.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 47
    ISSN: 0947-6539
    Keywords: chemotaxonomy ; diterpene metabolites ; dolabellanes ; marine natural products ; oxetanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6,8-Dimethyl-2,7-dioxatricyclo[4.2.13,8]nonan-4β-ol (9aβ) has been prepared from readily accessible starting materials in eight steps (14% overall yield). The parent dioxatricyclic framework 11 was obtained from 1,5-dimethyl-8-oxabicyclo[3.2.1]oct-3-en-6α-ol (7) in six steps (28% yield with respect to 7). Based on the experimental introduction of the oxetane moiety in vitro, a biosynthetic pathway is proposed for dictyoxetane (1) from a known dolabellane metabolite.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 48
    ISSN: 0947-6539
    Keywords: exchange coupling ; ferromagnetic properties ; ligand design ; magnetic properties ; multimetallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An approach is suggested for using ligands to control exchange coupling in multinuclear ions. The idea arose from structural, EPR, and magnetic studies of [PPh4]3 (Scheme 1). Ferromagnetic coupling has been found between the CoII and each CoIII in 3 with J = -22 ± 5 cm-1 (JS1 · S2). It is suggested that dominant antiferromagnetic superexchange is absent because of the strong σ-donor capacity of the tetradentate ligand [k4-PAC*]4- (Fig. 1). The ligand interacts at CoIII primarily with a single d orbital; it is thus best able to participate in superexchange. The interaction makes the unique d orbital strongly σ-antibonding and empty for each d6, S = 1, CoIII ion in 3, that is, unavailable for antiferromagnetic coupling, but available for ferromagnetic pathways by a Goodenough-Kanamori mechanism. By corollary, when any [k4-PAC*]4--type ligand with any magnetic ion Ma in the tetradentate site binds any magnetic ion Mb in the bidentate site, ferromagnetic coupling should be favored provided Ma is not a d9 ion.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 49
    ISSN: 0947-6539
    Keywords: dinitrogen complexes ; EPR spectroscopy ; iron compounds ; reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of [Fe(CO)2-L2X2] (L = P(OMe)3 X = Br (1a), I (1b); L = P(OiPr)3, X = Br (2a), I (2b); L = PEt3, X = Br (3a), I (3b)) with Zn in dioxane (1a,b-2a,b) or PhLi in ether (3a,b) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe)3, X = Br (4a), I (4b); L = P(OiPr)3, X = Br (5a), I (5b); L = PEt3, X = Br (6a), I (6b)). Slightly contaminated 5a,b and pure 6a,b were isolated as stable crystalline blue or blue-green complexes. Complexes 4a,b were obtained, with only minor impurities, by comproportionation of 1a,b and the dicarbonyl(halo)bis-(trimethylphosphite)ferrate anions 7a,b and characterized in THF solution. The comproportionation products 5a,b-6a,b were obtained in high yields by reaction of 2a,b-3a,b with the dinitrogen complexes 13-15. Further reduction of 4a,b-6a,b or exhaustive reduction of 1a,b-3a,b with sodium amalgam or iBuLi in THF afforded the nonisolable dicarbonyl-(halo)bis(phosphorus donor)ferrate(o) anions (7a,b-9a,b). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable dicarbonyl (halo) hydridobis (phosphorus donor)iron(II) complexes (L = P(OMe)3, X = Br (10a), I (10b); L = P(OiPr)3, X = Br (11a), I (11b);L = PEt3, X = Br (12a), I (12b)). In the presence of N2, 8a was transformed into dinitrogen complex [Fe(CO)2{P(OiPr)3}2N2] (13). With 9a,b the reaction led to formation of [Fe-(CO)2(PEt3)2)2N2] (14) and [{Fe(CO)2-(PEt3)2}2(μ-N2)] (15). In solution at low temperature (-90 to 0°C), the dinitrogen complexes 14 and 15 are in equilibrium with each other. Complexes 13, 14, and 15 were characterized by IR, 1H, 13C, 31P, and 15N NMR spectroscopy. The structures of 5a, 6b, 14, and 15 were determined by X-ray diffraction studies.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 50
    ISSN: 0947-6539
    Keywords: aniline ; aromatization ; hydrogen transfer ; mechanistic studies ; radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitro-, nitroso- and azobenzene are reduced almost quantitatively to aniline when heated to 230-300°C with 9,10-dihydroanthracene (DHA), xanthene or tetralin. From the effect of polar substituents and polar solvents on the reactivity and from the isotope effect kH/kD ≍ 2.4 (280°C), a hydrogen-atom transfer from the H donor to the acceptor (retrodisproportionation) is proposed as the rate-determining step. The lower reactivity of xanthene compared with 9,10-dihydroanthracene eliminates the possibility of a rate-determining hydride transfer. The observation of an intense ESR signal of 9-xanthyl radicals during the reaction in diphenyl ether and the typical products support the proposed homolytic mechanism.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 51
    ISSN: 0947-6539
    Keywords: bridging ligands ; coordination ; copper compounds ; exchange coupling ; magnetic properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Magnetic long-range exchange coupling between two unpaired electrons of two copper(II) ions in a square-pyramidal ligand environment (dx2-y2)1, which are rigidly separated by 〉 10 Å by an organic spacer ligand (e.g., a μ-dicarboxylato ligand) has been systematically studied. The following complexes have been synthesized: [{LCu(OH2)}2(μ-terephthalato)](ClO4)2 (I), [LCuII(OH2)(benzoato)](CIO4) (2), [{LCuII(NCS)}2(μ-terephthalato)]-2 CH3OH (3), [{LCuII(NCS)}2 (μ-4,4′-oxybisbenzoato)] · 3 CH3OH (4), [{LCuII(OH2)}2 (μ-tetrafluoroterephthalato)](CIO4)2 (5), [{LCuII(OH2)}2{LCuII}2 (μ-tetrafluorobenzoato)3](CIO4)2 · 6 H2O (6), [{LCuII(OH2)}2 (μ-biphenyl-4,4′-dicarboxylato)](CIO4)2 (7), [LCuII(μ-biphenyl-4,4′-dicarboxylato)]n (HZO)2n (8), [{LCuII(NCS)}2 (μ-biphenyl-4.4′-dicarboxylato)] (9), [{LCu(OH2)}2, (μ-trans,trans-2,4-hexadien1,6-dicarboxylato)] (CIO4)2 (10) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane). Complexes 1, 2, 3, 4, and 6 have been characterized by X-ray crystallography; the structure of 1 has been described previously.[15] Temperature-dependent magnetic susceptibility data for all complexes have been measured over the range 2.0-298 K. In complexes 2, 3, 4, 6, 8, and 9 only very weak, if any, intermolecular antiferromagnetic or, in the case of 6, ferromagnetic coupling has been observed (|J|≤2cm-1; H= -2JS1 S2 S1 = S2 = 1/2). In contrast, in complexes 5 (2J=-80cm-1), 7(2J=-62cm-1), and 10 (2J = -100 cm-1) relatively strong intramolecular antiferromagnetic exchange coupling has been detected. The intramolecular Cu…Cu separation is 11.3Å in 5, 15.6 Å in 7, and approximately 12.0Å in 10. These data demonstrate that intramolecular antiferromagnetic exchange coupling of considerable magnitude is possible over distances 〉 15 Å, provided that the effective magnetic orbitals are favorably aligned.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 52
    ISSN: 0947-6539
    Keywords: copper compounds ; exchange coupling ; heterometallic compounds ; lanthanide compounds ; magnetic properties ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and structural characterisation of three copper-lanthanoid complexes are reported. The compounds, of general formula [Cu3M(chp)8(NO3)(S)] [M = Gd, S = H2O in 2; M = Dy, S = H2O in 3; M = Er, S = (H2O)0.5(MeOH)0.5 in 4; chp = anion of 6-chloro-2-pyridone], are made by reaction of [Cu2(chp)4] (1) with the hydrated lanthanoid nitrate salt in methanol. Structural studies reveal the three copper atoms lie in an approximate hemisphere about a central lanthanoid atom. Magnetic studies on 2 and two further Cu-Gd complexes show ferromagnetic coupling between the 3d and 4f metals. Consideration of these results along with magnetic data previously reported for Cu-Gd compounds leads to a correlation between the magnitude of this exchange coupling and the exponential of the Cu…Gd distance. This is the first magneto-structural correlation reported for mixed d-block/f-block metal complexes.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 53
    ISSN: 0947-6539
    Keywords: conjugation ; connectivity ; electronic coupling ; metalloporphyrins ; photosynthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the regulation of the photophysical properties of highly conjugated porphyrin arrays is described. The absorptive and emissive signatures of such supramolecular structures can be modulated to an impressive degree by regulation of: i) the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores, and ii) the magnitude of ground state chromophore-chromophore electronic communication within the supermolecule. The power of this approach is illustrated by the straightforward synthesis as well as the electronic and emission spectra of eight different porphyrin arrays in which (5,10,15,20-tetraphenylporphinato)zinc(11) and (10,20-diphenylporphinato)zinc(11) complexes are joined by ethyne or butadiyne groups. The points of connectivity of these bridges between the chromophoric building blocks are systematically varied to produce a series of supramolecular structures with meso-to-meso, meso-to-β, or β-to-β linkage topologies. These variations allow excellent control of the ground- and excited-state characteristics of the arrays in the series by regulating the degree of both excitonic and electronic porphyrin-to-porphyrin coupling. Our approach shows the precision with which photophysical properties can be engineered in appropriately designed supramolecular systems.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 54
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 161-164 
    ISSN: 0947-6539
    Keywords: block synthesis ; epoxidations ; glycosylations ; oligosaccharides ; selenoglycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several suitable building blocks for the construction of the phytoalexin elicitor α-methyl-32, 34-di-β-D-glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals. Block coupling of trimeric phenylseleno- and ethylthioglucosyl donors 17 and 18 with tetrasaccharide 16 in the presence of the thiophilic promoter N-iodosuccinimide and catalytic trifluoromethanesulfonic acid furnished the desired heptaglucan 2 in high overall yield.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 165-170 
    ISSN: 0947-6539
    Keywords: acid leaching ; deintercalation ; layered oxides ; metastable oxides ; molybdenum compounds ; tungsten compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deintercalation of amines from the layered amine adducts of WO3, MoO3 and W1-xMoxO3 has been employed as a soft chemical route to produce unusual metastable structures of the oxides. After the adducts of WO3, MoO3 and W1-xMoxO3 (x = 0.25, 0.5, 0.75) with amines such as triethylamine (TEA), pyridine, n-butylamine and n-octylamine had been characterized, deintercalation was carried out thermally as well as by acid leaching. Thermal deintercalation yielded novel metastable structures of WO3 and MoO3 that were significantly different from the stable forms, which contain distorted metal-oxygen octahedra. Thus, ReO3-type cubic WO3 was obtained by the thermal deintercalation of WO3 · 0.5 TEA. Acid leaching of the amines gave metastable phases of WO3, MoO3 and W1-xMoxO3, which were different from those obtained thermally. All the metastable phases transformed to the corresponding stable forms at higher temperatures.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 56
    ISSN: 0947-6539
    Keywords: diarylethenes ; molecular devices ; nonlinear optics ; photochromes ; redox switches ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic photochromic systems represent a starting point for the elaboration of light-triggered molecular switching devices. The novel bispyridinium and bispyridine compounds 12+ and 6 were synthesized as their uncyclized isomers from 3,5-dibromo-2-methylthiophene in overall yields of 43 and 44%, respectively. The diarylethene photochromes 2 and 10-13, substituted with electron donors and acceptors, were prepared from 5-methylthiophene-2-carboxaldehyde in 21-32% overall yield. All of the compounds were found to exhibit pronounced photochromic properties. Irradiation with UV light resulted in essentially complete photocyclization of the open forms to the intensely coloured closed isomers which could, in turn, be reconverted back to the open state with visible light of γ〉600 nm. The absorption maxima of the described compounds in their closed forms are shifted far towards, and even into, the near-IR region. Whereas no thermochromic properties were observed for the open isomers, the rates of thermal decolouration of the cyclized forms was found to be highly dependent on the nature of the substituents on the thiophene rings. It was demonstrated that reversible photochemical interconversion between the two photochromic states could be used to effectively switch a number of physical properties. Thus, the molecules 12+ and 12 represent two kinds of redox switches, the former in reduction and the latter in oxidation, in which electron conduction is switched on in the closed state and off in the open state. Compound 12 may also be considered to be a photoswitchable analogue of tetrathiafulvalene type substances. On the other hand, compound 2 displays a marked increase in nonlinear optical activity on conversion from the open to the closed form. Such systems are prototypes of photoswitchable molecular wires where electron conduction and push-pull interaction can be reversibly modulated by an external stimulus, namely, irradiation by light.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 57
    ISSN: 0947-6539
    Keywords: electrophilic additions ; N-pyrrolyl complexes ; rearrangements ; rhenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of [{Re}(OTf)] (1; {Re}  -  (η5-C5H5)Re(NO)(PPh3) and potassium pyrrolide gives the N-pyrrolyl complex 2, 88%). Reactions of 2 with (CF3CO)2O/N(C2H5)3 and CH3O2CC=CCO2CH3 give 3- and 2-substituted pyrrolyl complexes respectively (3, R/R′ = H/COCF3, 77%; 5, R/R′ = C(CO2CH3)=CHCO2CH3/H, 69-87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF4·OEt2 give the 2H-pyrrole adducts +X- (7+X-; 89-83%). At 0-25°C in CH2Cl2, these rearrange to the carbon-ligated tautomers +X-(8+X-) and then +X-; (9+X-; 72-96 h, 90-96%). Reaction of 1 and pyrrole in refluxing toluene gives 8+TfO- and then 9-TfO- (92%). However, 1 and pyrrole react too slowly in CH2Cl2 to be intermediates in the conversion of 7+TfO- to 9+TfO-. Reaction of 9+ TfO- and KH gives the C-pyrrolyl complex (68%), which adds TfOH to give 9+TfO-. Mechanistic aspects of the preceding reactions are discussed. The crystal structures of 2 and 9+TfO- are determined, and the NC4Hx ligand conformations analyzed with extended Hückel MO calculations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 58
    ISSN: 0947-6539
    Keywords: diarylethenes ; electrochromes ; molecular devices ; optical memory ; photochromes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bisphenolic dithienylethene molecules 1a and 1b were synthesized in overall yields of 45% from 4-bromoanisole and 44% from 2.6-di-tert-butyl-4-iodophenol, respectively. The corresponding extended quinones 3a and 3b were also prepared. Photochemical studies showed that compounds 1 are photochromic; the open forms 1 could be converted with UV light of 312nm to the closed coloured forms 2 with photostationary states lying at essentially complete conversion (〉 98%). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stability for both photoisomers. Cyclic voltammetry studies involving the 2/3 couples showed that whereas 2b undergoes irreversible oxidation at + 0.85 V (vs. SCE in THF), the hydroquinone 2a is reversibly oxidized at an E1/2 of + 0.72V (in MeCN, quasi-reversibly in THF at + 0.81 V); this reflects the differences in deprotonation behaviour of the generated QH2/2+ species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properties. In a complementary fashion, redox switching of the photochromic properties within the 2a-3a pair is possible since 3a is stable to visible light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- and electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the basis for an optical memory system with multiple storage and nondestructive readout capacity through a write-lock-read-unlock-erase cycle.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 59
    ISSN: 0947-6539
    Keywords: alcohols ; amphiphiles ; GID ; ice nucleators ; monolayers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic analysis of grazing incidence synchrotron X-ray diffraction data of uncompressed amphiphilic alcohols CnH2n+1 OH (n = 31, 30, 23, 20, 19, 18, 16, 14, 13) on a water subphase at 5°C is presented. Pronounced structural changes were observed on reduction of chain length from n = 31 to 13. The relative amount of two dimensional (2-D) crystalline material formed fell drastically; shorter crystalline coherence lengths were also observed. For n-31-18 the molecules are arranged in a rectangular cell (a ≈ 5 Å, b increases from ca. 7.4 to ca. 8.2 Å) with plane symmetry p1 g1. For n 〈 18 a tilted free-rotator phase is probably adopted. The two glide-related molecules in the unit cell form a herringbone arrangement in which the chain axes are parallel and separated by [(a + b)/2]. The molecular chains are tilted from the vertical in the b direction; the tilt angle increases from ca. 7° to ca. 21° over the range n = 31 to 19, and then drops to 12° for n = 13. There is a continuous increase in molecular cross-sectional area from 18.4 to 20.3 Å2 and in the atomic displacement parameter parallel to the water surface; it increases from 0.1 Å2 for n = 31 to 0.30 Å2 for n = 19. We explain the preference for chain tilt along the b axis, rather than a, in terms of hydrogen bonding to the water subphase. The various structural properties of the CnH2n+2OH (n = 31-13) monolayer series, such as degree of crystallinity and coherence length, lattice dimensions, chain orientation, and molecular motion, may be correlated with the ice-nucleating efficiency of these alcohol monolayers as a function of n.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 60
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 61
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 62
    ISSN: 0947-6539
    Keywords: rapamycin ; stannylethenes ; Stille coupling ; vinyl iodides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Details of the total synthesis of rapamycin (1) are reported. The synthesis required the preparation of intermediates 4 - 9 in nonracemic form; key coupling reactions included a chromium-mediated addition of vinyl iodide 8 to aldehyde 7 and an Evans aldol reaction to couple fragments 62 and 9. Intermediates 4 and 6 were joined through an amide bond formation to afford advanced intermediate 71. Swern oxidation of the diol in 71 was followed by a selective removal of the TES groups and a second Swern oxidation. Finally, removal of the remaining silyl protecting groups provided fully deprotected, penultimate intermediate 2 in which all carbons were in their proper oxidation state. Macrocyclization was achieved through a tandem inter/intramolecular palladium-mediated Stille coupling reaction between distannylethene 3 and bis(vinyl iodide) 2. This latter process accomplished in one step the installation of the remaining two carbons of the natural product and the completion of its total synthesis.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 63
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 64
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; alkenylations ; SAMP/RAMP hydrazones ; selenyl aldehydes ; sphingosine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-threo-sphingosine and its D-erythro isomer (1) are subunits of many glycosphingolipids, gangliosides and ceramides. This paper describes the highly diastereo- and enantioselective synthesis of both isomers (de, ee 〉 98%). The key steps in the synthesis are the aldol reaction of the SAMP hydrazone (S)-2 with racemic α-phenylselenylpentadecanal 3, the diastereoselective triacetoxyborohydride reduction of ketone 5 and exclusive (E) C—C double bond formation in the elimination of hydroxyl and selenyl moieties promoted by methanesulfonyl chloride. Mesylate 8 was then readily converted via the 1,3-O-acetonide-protected azidosphingosine 9 to L-threo-sphingosine. Conversion to the known 1-O,2-N-diacetyl-protected sphingosine 13 with subsequent Mitsunobu inversion of the C3—OH centre afforded the D-erythro-sphingosine epimer.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 389-393 
    ISSN: 0947-6539
    Keywords: crystal structure ; differential thermal analysis ; nitrogen oxides ; phase transitions ; twinning ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of N2O3 and N2O4 have been prepared from measured volumes of NO and O2. Phase relationships in the system N2O3/N2O4, which depend on the composition of the samples and on the temperature, were studied by the Guinier technique and differential thermal analysis. Single crystals of phases A and B of N2O3 were grown in situ on a diffractometer and studied at temperatures between -107 and -170°C by X-ray diffraction. The structure analysis of A-N2O3 (tetragonal, space group I41/a, T = -170°C, a = 1625.57 (16), c = 880.49(13) pm, Z = 32, R1 = 0.051 for 1030 unique reflections) is hampered by twinning and additional disorder of one of two crystallographically independent molecules. B-N2O3 is nicely ordered with one molecule in the asymmetric unit (orthorhombic, space group P212121, T = -160°C, a = 506.86(4), b = 647.96(5), c = 863.26(6) pm, Z = 4, R1 = 0.023 for 1352 unique reflections). The most interesting features of the N2O3 molecule are its planarity and the extraordinarily long N—N bond (189.0(1) pm).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 66
    ISSN: 0947-6539
    Keywords: cobalt compounds ; cyclopentadienyl ligands ; metallocenes ; peralkylations ; rhodium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acidity of methyl protons in the 18-electron cationic complexes [MCp*Cp]1PF6- and [MCp2*]+PF6- (M = Co or Rh, Cp = η5-C5H5, Cp* = η5- C5Me5) has been used for novel syntheses of starburst organometallic complexes. [CoCp*Cp]+PF6- was deprotonated at -30 °C with Si2Me6NK (1 equiv) in THF to give the fulvene complex [CoICp(η4-C5Me4CH2)]. This was not stable at 20°C, but was characterized by 1H and 13C NMR at -30 °C. The complexes [MCp*Cp]+PF6- (M = Co or Rh) reacted with excess base (KOH or tBuOK) and alkyl halides (RX = CH3I, C2H5I, CH2=CHCH2Br, or PhCH2Br) to give decasubstituted complexes (i.e., two hydrogens of each methyl group are replaced by two R groups). Distinct endo and exo alkyl groups are observed in the new complexes by NMR at room temperature. Coalescence occurs at higher temperatures; this indicates that the bulky alkyl groups are rotating. The calculated activation parameters (ΔG≠) are 71.3±0.8, 70.3±0.8, and 81.0±0.8 kJmol-1 for [Co(C5iPr5)Cp]+PF6-, [Rh(C5iPr5)-Cp]+PF6- (in C6D5NO2), and [Co{C5-(CHEt2)5}Cp]+PF6 (in o-C6H4Cl2), respectively. The single directionality of these ligands is confirmed by the X-ray crystal structure of [Co(C5iPr5)Cp]+PF6. This structure clearly shows the “paddle wheel” conformation adopted in the C5iPr5 ligand, due to steric hindrance between adjacent isopropyl groups and the staggered conformation of the two rings. The relative E° values measured by cyclic voltammetry show that the electron-donating properties of the new C5(CHR2)5 ligand are between those of C5H5 and C5Me5- With the decamethylcobalticinium salt [CoCp2*]+PF6-, the permethylation reactions with base and CH3 I did not go to completion, even under forcing conditions and with repeated reaction (the maximum number of methyl groups introduced was 14). On the other hand, [RhCp2*]+PF6-, in which the distance between rings is larger than in the Co analogue, reacted with excess KOH and CH3I to give [Rh(C5iPr5)2]+PF6 in 55% yield; only one diastereoisomer was detected by NMR (ΔG≠ = 85.5±0.8 kJ mol-1 in C6D5NO2). The C5iPr5 sandwich complexes are extremely robust, even at the 19-electron (CoII) stage. The 20-electron K+ salt of the CoI anion was regiospecifically protonated by H2O at the Cp ligand to give [Co(C5iPr5)(η4-C5H6)] and was decomplexed at 190°C to K+(C5iPr5)-.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 67
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 68
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 69
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 403-413 
    ISSN: 0947-6539
    Keywords: conjugation ; ferromagnetism ; helices ; magnetic properties ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structures of conjugated polymers containing methyl radicals, carbenes, and nitrogen-based radicals coupled in various ways through benzene rings are examined, employing band-structure calculations in the extended Hückel approximation. The structural and electronic properties of polymers with a para-phenylene or meta-phenylene coupling unit are compared. In the polymer with methyl radicals coupled through a para-phenylene unit, a pairing or Peierls distortion occurs to remove the degeneracy at the Fermi level. The resulting bandgap is nevertheless relatively small; we conclude that such polymers are likely to exhibit high electrical conductivity upon doping, very much like polyacetylene. On the other hand, in the polymers with a meta-phenylene coupling unit, striking symmetry-determined, halfoccupied narrow bands appear at the Fermi level and contribute to the stability of the ferromagnetic state. The relation of a potential ferromagnetic state to metallic, CDW, and SDW states is discussed from the viewpoint of orbital interactions in extended systems. We suggest novel 3- and 4-fold helical structures for the meta-phenylene-coupled polymers.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 70
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 430-435 
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric synthesis ; BNCT ; carboranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two α-amino acids containing the 1,2-dicarba-closo-dodecaborane (12) cage, namely, 5-(1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (1) and 5-(2-methyl-1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (2), were prepared by asymmetric synthesis (e.p. 〉 98%) by using the chiral glycine equivalent, imidazolidinone 3, introduced by Seebach, and Oppolzer's camphor-derived sultam derivative 4. The dextrorotatory enantiomers (sodium D line in methanol) of the amino acids 1 and 2 were both shown to have (S) configuration.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 71
    ISSN: 0947-6539
    Keywords: biomineralization ; calcite ; crystal morphology ; mosaic structure ; symmetry reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organisms can exert a remarkable degree of control over crystal growth. One way of achieving this is by the adsorption of specialized macromolecules on specific planes of the growing crystals. With continued growth of the crystal, the macromolecules are incorporated inside the crystal bulk. Their presence does not change the crystal structure, but creates discontinuities in the perfect lattice. Here we study in detail three unusual cases of reduction in symmetry at the level of crystal domain shapes, induced by this controlled intercalation. We examined sponge spicules, which are single crystals of Mg-bearing calcite. They were specifically chosen for this study, because their morphologies do not reflect the hexagonal symmetry of calcite. Their crystal textures (coherence lengths and angular spreads) were characterized by high-resolution X-ray diffraction with well-collimated synchrotron radiation. The results are compared to analogous studies of synthetic calcite and Mg-bearing calcite. In all the selected spicules reduction in symmetry is observed in the coherence lengths among symmetry-related crystallographic directions. The reconstructed shapes of the domains of perfect structure closely match the specific spicule morphologies. The synthetic crystals show no such reduction in symmetry. Although the manner by which such exquisite control is achieved is not known, we envisage it involving a combination of oriented nucleation with either physical or stereochemically driven adsorption.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 72
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 423-429 
    ISSN: 0947-6539
    Keywords: kinetics ; peroxyl radicals ; pulse radiolysis ; radicals ; superoxide radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxyl radicals were generated radiolytically and reacted with a number of benzene derivatives (PhH). In the presence of oxygen, the hydroxycyclohexadienyl radicals thus formed were converted into their corresponding peroxyl radicals. Pulse radiolysis has shown the oxygen addition (forward reaction, f) to be reversible (reverse reaction, r) [Eq. (1)]. The peroxyl radicals can eliminate HO2· to yield phenols, alongside some ring-fragmentation products (product-forming reaction, p). The rate constants for the forward and reverse reactions (kf and kr) and the corresponding stability constants K (= kf/kr) were determined for the hydroxy-cyclohexadienyl radicals derived from anisole, toluene, fluorobenzene, benzene, chlorobenzene, benzyl chloride, benzoate ion, phenylalanine, and terephthalate ion. The constants kf lie between 8 × 108 (anisole) and 1.6 × 107 dm3 mol-1 s-1 (terephthalate ion), and kr between 7.5 × 104 (toluene) and 3.4 × 103 s-1 (terephthalate ion). The stability constants lie between 2.6 × 104 (benzene) and 3.3 × 103 dm3 mol-1 (phenylalanine). The rate constants for the product-forming reactions kp are between 5.5 × 103 (anisole) and 3.4 × 102 s-1 (benzoate). For the peroxyl radical derived from phenylalanine, a bond dissociation energy of 5.5 kcal mol-1 has been derived. A number of hydroxy-cyclohexadienyl radicals (e.g., those derived from benzoic acid, ethylbenzoate, benzonitrile, and nitrobenzene) react too slowly to allow the equilibrium constant to be determined by means of pulse radiolysis. These reactions have rate constants kf in the order of 5 × 106 dm3 mol-1 s-1, except for nitrobenzene where the reaction is too slow for measurement. The rate constants kr are below 500 s-1, and the product-forming reaction is too slow to be detected by pulse radiolysis. γ-Radiolysis of N2O/O2(4:1)-saturated aqueous solutions of benzonitrile gave dimeric compounds (e.g., dicyanobiphenyls) in low yield, alongside the three isomeric phenols; this again proves the low reactivity of its hydroxycyclohexadienyl radical toward oxygen.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 73
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 449-453 
    ISSN: 0947-6539
    Keywords: computer chemistry ; databases indexing ; reaction organization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A logical system is presented to describe organic reactions. It is based on the net structural change in a reaction, rather than on substructure searching. This system rigorously provides a place for any reaction. It is very simple to use by hand, but, since it is also numerical, it provides a basis for organizing and retrieving reactions in a database by computer. The effectiveness of a program, COGNOS, written to implement and test the system on a large database, lends confidence in this logic for organizing reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 74
    ISSN: 0947-6539
    Keywords: biphenyls ; bipyridinium salts ; conformation ; semiempirical calculations ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of substituted N-aminopyridinium compounds yields bipyridinium salts. After anion exchange Br- → CIO4-, it was possible to grow single crystals from the 4,4′-di(tert-butyl) derivative. The structure determined at 100 K shows a dihedral angle of 84° between the molecular halves connected by a shortened N—N bond of 143 pm in length. This result is contrary to that expected from the isoelectronic correspondence 〉C—C〈↔〉N—N〈, which would suggest planarity, as has been observed experimentally both in solid biphenyl, and in tetraalkylhydrazine dications and radical cations. Lattice packing analysis, however, reveals the presence of hydrogen bonds C(H)…O between the phenyl rings and the perchlorate anions. AM 1 enthalpy hypersurface calculations for the isoelectronic series H5C5X-YC5H5 (X-Y = C—C, +N—C, +N—N+, -B—N+, B—C, and B—B-) predict single-minimum potentials for both the dication 〉N—N〈 as well as the dianion 〉B—B〈 with the molecular halves twisted perpendicular to each other. In detailed model calculations, counteracting effects of π electron density delocalization vs. H/H repulsion of the ortho ring hydrogens adjacent to the central bond seem to dictate the delicate balance of the biphenyl twisting. For further experimental confirmation, the structure of the isosteric molecule 4,4′-di(tert-butyl)biphenyl has been determined: in contrast to the unsubstituted π hydrocarbon with a latticeenforced dihedral angle of 0°, close to the calculated value, the two molecular halves are twisted by 40° - as in biphenyl in the gas phase.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 75
    ISSN: 0947-6539
    Keywords: electron transfer ; iron-sulfur proteins ; NMR spectroscopy ; proteins ; solution structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the 1H NMR spectrum of the oxidized form of the high-potential iron-sulfur protein (HiPIPI) from Ectothiorhodospira halophila, 91% of the total proton resonances and 100% of the residues have been assigned. The standard COSY, NOESY, and TOCSY sequences have been optimized for the paramagnetism of the molecule. Extensive assignment of the 15N NMR spectrum has been obtained through HMQC spectra. With 1437 dipolar connectivities, of which about 10% involved fast-relaxing protons, a family of 18 structures was generated with an RMSD of 0.65 Å by using the programs developed by Wüthrich. The family of structures was further refined by various calculation steps; the final RMSD was 0.48 Å. The structures appear to be very similar but not equal to the structures of the reduced protein. Despite the similarity in structure, significant variations in the chemical shifts are observed. A similar behavior was observed for the homologous protein from Chromatium vinosum. It is concluded that NMR is a sensitive tool to monitor differences between oxidized and reduced proteins; however, the detailed structural variations should be evaluated with caution at the present level of resolution, which roughly corresponds to a resolution of 2.5 Å in an X-ray structure.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 76
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 634-636 
    ISSN: 0947-6539
    Keywords: carbasugars ; cyclitols ; enzyme inhibitors ; salbostain ; total syntheses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of trehalase inhibitor salbostatin (1), recently discovered as a novel metabolite of Streptomyces albus species, has been achieved starting from the major product (58 % yield) from the coupling of the amine di-O-isopropylidene-α-valienamine and the electrophile 1,5 : 2,3-dianhydro-D-mannitol in 2-propanol. Deprotection with aqueous acetic acid and subsequent purification on a column of acidic resin afforded 1, which showed inhibitory activity (IC50 = 8.3 μML-1) against silkworm trehalase.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 77
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 619-624 
    ISSN: 0947-6539
    Keywords: alkenes ; carbenoids ; carbolithiations ; cyclopropanations ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical course of the intramolecular carbenoid cyclopropanation reaction has been studied for the epimeric carbenoids 12a and 12b. In these reactions the tert-butyldimethylsilyloxy substituent serves as an internal stereochemical reference point. It was found that 12b cyclizes rapidly at -110°C in a complexation-assisted concerted process to give the bicyclo[3.1.0]hexane 16. The diastereomer 12a cyclizes more slowly at -100°C to give both 16 and 17; the former is probably formed by a complexation-assisted carbolithiation pathway.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 78
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; azomethine ylides ; chiral auxiliaries ; cycloadditions ; pyrrolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon treatment with triethylamine or DBU in the presence of LiBr, aromatic and aliphatic imines of amino acid esters are converted to N-metalated azomethine ylides. These 1,3-dipoles undergo highly stereoselective cycloadditions with N-acryloyl-(S)-proline esters in THF at -78 to -40°C to afford highly substituted pyrrolidines with complete regiocontrol and good to excellent diastereomeric ratios. The chiral auxiliary groups can readily be removed from the cycloadducts by simple acid hydrolysis. To rationalize the observed stereoselectivity a transition-state model is proposed in which the lithium cation is coordinated to both the 1,3-dipole and the dipolarophile.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 79
    ISSN: 0947-6539
    Keywords: chelate ligands ; dioxygen activation ; EPR spectroscopy ; redox systems ; SQUID ; zeolites ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intrazeolitic transition metals, such as Ni2+ and Co2+, were chelated by open or closed, tetra- or pentadentate polyamine ligands. Their coordination and redox chemistry was studied by IR-Raman, EPR, diffuse reflectance, and magnetic techniques. For pseudo-octahedral complexes with tetradentate ligands, the presence of the zeolite favors cis coordination over the trans form. This is explained by the very low tendency of the zeolite surface to bind as a monodentate ligand to a planar metal complex. However, if trans complexes are formed (as with Ni2+), the axial positions on the complex are available for ligand exchange. Such intracrystalline complex syntheses result in the formation of new redox solids. For example, [CoII-(cyclam)]2+-NaY (cyclam = 1,4,8,11-tetraazacyclotetradecane) is a reversible, high-affinity (p1/2〈1 mbar) and high-capacity (〉90 μmol g-1) dioxygen-sorbing material.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 80
    ISSN: 0947-6539
    Keywords: aggregates ; asymmetric syntheses ; stereochemistry ; sulfoximines ; zinc enolates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation, structural characterization, and reactivity of ethylzinc-containing enolates and organometallics derived from β-carbonyl sulfoximines are reported. X-ray crystal structures show significant differences between aggregated species obtained from β-keto and β-amido sulfoximines. Whereas the former gives an O-metalated ethylzinc enolate, the latter crystallizes as C-metalated carbonyl species. NMR investigations reveal the presence of chelated zinc enolates in solution. The relationship between structure and reactivity is demonstrated by the reaction profiles of the ethylzinc-containing compounds. A high diastereoselectivity (〉 90% de) was observed in the aldol reaction between the metalated β-amido sulfoximine and benzaldehyde in the presence of trimethylsilyl chloride.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 81
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 82
    ISSN: 0947-6539
    Keywords: ate complexes ; intramolecular coordination ; lutetium complexes ; organometallic compounds ; yttrium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New complexes of lutetium and yttrium containing the monoanionic, terdentate ligand [2,6-(Me2NCH2)2C6H3]- (NCN) have been synthesized by substitution reactions starting from MCl3 (M = Lu, Y). Reaction of MCl3 (M = Y, Lu) with one equivalent of (NCN)Li affords the ate complexes [(NCN)MCl2(μ-Cl)(μ-Li(thf)2)]2) (M = Lu (1a), Y (1b)) in which the terdentate ligand is bound in mer fashion and all three chloride atoms are retained in the product. Crystals of 1a are monoclinic (space group P21/n, a =10.4559(4), b = 21.6150(9), c=12.1700(7) Å, β = 105.294(4)°, Z = 2, final R = 0.039 for 3695 observed reflections [I〉2.50σ(I)]). Attempted substitution of chloride in the yttrium complex 1b by Me3SiCH2- leads to decomposition. However, reaction of 1a with Me3SiCH2Li gives the monoalkyl complex [(NCN)Lu-(μ-Cl)(CH2SiMe3)]2 2, 30% yield), in which the terdentate ligand is bound in a pseudo-facial manner. Crystals of 2 are triclinic (space group P1, a = 9.8575(7), b = 10.0171(7), c = 11.1460(14) Å, α = 75.096(8). β = 78.092(8), γ =77.474(6)°, Z = 1, final R1 = 0.11 for 1361 reflections [I 2σ(I)]). Substitution of the chloride ions in 2 by Me3SiCH2- is possible and affords quantitatively the bisalkyl complex [(NCN)Lu(CH2SiMe3)2] (3). The lutetium complexes 2 and 3 are formally coordinatively unsaturated complexes, which are moisture-sensitive and thermally stable for several weeks when dissolved in aromatic solvents. However, they decompose rapidly in aliphatic solvents such as hexane, and a decomposition route involving the formation of carbene species is proposed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 83
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 454-466 
    ISSN: 0947-6539
    Keywords: antitumour agents ; balanol ; enzyme inhibitor ; natural product ; total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of balanol, a potent protein kinase C inhibitor isolated from the fungus Verticillium balanoides, is described. The hexahydroazepine fragment was prepared from D-serine through a sequence of reactions including the diastereoselective allylboration of a derived amino aldehyde and a base-induced 7-exo-tet ring closure as key steps. The benzophenone fragment was secured through the initial coupling of the two functionalised aromatic components through an ester linkage, followed by intramolecular nucleophilic attack of an aryl lithium derivative to form the desired ketone bridge. After coupling of the two balanol domains, the adoption of benzylderived protecting groups for the latent functionalities then allowed the liberation of balanol in a single step by catalytic hydrogenolysis. Finally, the newly developed synthetic strategy was applied to the synthesis of a variety of designed balanol analogues for biological evaluation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 84
    ISSN: 0947-6539
    Keywords: allylhydrazines ; cadmium compounds ; catalysis ; photochemistry ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Suspensions of zinc or cadmium sulfide powders in a protic solvent catalyse the linear addition of enol ethers and olefins to 1,2-diaryl- and 1-aryl-2-alkyl-1,2-diazenes, producing allylhydrazine derivatives. Relative quantum yields decrease sharply when the 1,2-diazene is more difficult to reduce, while their relationship to the oxidation potential of the enol ether/olefin is complicated. Reduction to 1,2-diarylhydrazine and concomitant dehydrodimerization of the enol ether occurs as a side reaction. It is favoured by increasing light intensity and becomes the major reaction path when platinized (5 mol%) photocatalysts are employed. It is proposed that the photogenerated electron-hole pair in a proton-coupled electron transfer reduces the diazene to a hydrazyl radical and oxidizes the olefin/enol ether to a radical cation. The allylic radical obtained from the latter by deprotonation then undergoes C—N coupling with the hydrazyl radical to afford the allylhydrazine. Diarylhydrazine formation occurs by disproportionation of the hydrazyl radical or by a successive proton-coupled reduction. Thus photoaddition can be classified as a 1 e-/1 h+ process while 2e-/2h+ are necessary for the reduction.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 85
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 86
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 87
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 88
    ISSN: 0947-6539
    Keywords: asymmetric ; syntheses ; enzyme inhibitors ; squalestatins ; total syntheses ; zaragozic acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel synthetic approach to the construction of the zaragozic acids, which was used for the asymmetric synthesis of zaragozic acid A/squalestatin S1 (1), is described. Fragment 5, representing the tricarboxylic acid core portion, is assembled in three key steps: 1) Stille coupling to establish the carbon framework; 2) enantioselective dihydroxylation to introduce the absolute stereochemistry; and 3) diastereoselective dihydroxylation to complete the required carbon-oxygen connectivity. The convergency of this synthesis is demonstrated by the dithiane addition of a variety of C 1 side chains (e.g., 78) to advanced intermediate 5. A multi-event acid-catalyzed rearrangement yielded the zaragozic acid core 86, which was converted to an intermediate obtained from degradation of zaragozic acid A. A second-generation synthesis of the core of the zaragozic acids is also described. When aldehyde 90 was used instead of 5, both the yield and diastereoselectivity of the dithiane addition reaction were improved, although the degree of convergency was slightly lower.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 89
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general method for the homologation of aldehydes to α-amino aldehydes (aminohomologation) has been developed, which employs nitrones as iminium derivatives of the aldehydes. Key operations include a) the addition of a thiazole metalated at C-2 to the N-benzylnitrone derived from the aldehyde, b) the reductive dehydroxylation of the resultant thiazolyl N-benzylhydroxylamine, and c) the unmasking of the formyl group from the thiazole ring. The homologation sequence was studied by employing nitrones derived from various chiral polyalkoxy aldehydes and dialdoses. The addition of 2-lithiothiazole to these nitrones was syn-selective, whereas the reaction with the same nitrones precomplexed with Lewis acids was anti-selective. Hence, from each nitrone a pair of diastereoisomeric hydroxylamines was obtained. These compounds were then converted by the above sequence into α-epimeric α-amino aldehydes. Model elaborations of some of these products afforded the amino sugars D-glucosamine, D-mannosamine, D-nojirimycin, and advanced intermediates for the synthesis of destomic acid and lincosamine.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 90
    ISSN: 0947-6539
    Keywords: carbonyl ligands ; organometallic compounds ; phosphorus ligands ; tantalum compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of [TaCl5] by six equivalents of alkali metal naphthalenide in 1,2-dimethoxyethane at -60°C followed by treatment with gaseous PF3 provides the first homoleptic phosphane complex containing tantalum in the -1 oxidation state, [Ta(PF3)6]-. This can be protonated by concentrated sulfuric acid to yield the previously unknown highly acidic and volatile hydride [HTa(PF3)6]. An improved normal-pressure synthesis of [Ta(CO)6]- is described. Reduction of the latter species by sodium in liquid ammonia gives the carbonyl trianion [Ta(CO)5]3- which undergoes monoprotonation and stannylation to form [HTa(CO)5]2- and [Ph3SnTa(CO)5]2-, respectively. The hydride is a useful precursor to [(Ph3PAu)3Ta(CO)5], the only known gold cluster of tantalum.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 91
    ISSN: 0947-6539
    Keywords: amino alcohols ; asymmetric syntheses ; chiral auxiliaries ; enantiomeric resolution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically active tert-leucinol is an important building block in asymmetric synthesis. However, the (R) enantiomer particularly has so far remained difficult to obtain, mainly because of the laborious synthesis of the precursor amino acid, (R)-tert-leucine. Here we present a new, classical resolution of racemic tert-leucinol, which allows straightforward preparation of each, but especially the (R) enantiomer, in good yields and high optical purities. The feasibility of the synthesis of useful derivatives is demonstrated by transformation into the corresponding (R)-4-tert-butyl-2-oxazolidinone.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 92
    ISSN: 0947-6539
    Keywords: alkenyl ; Fischer-Tropsch synthesis ; labelling studies ; rhodium compounds ; vinyl ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results consistent with the participation of vinyls in the initiation and of alkenyl species in the propagation steps of the Fischer-Tropsch reaction are reported. Substantial incorporation of 13C2 into the alkene and alkane (C3-C7) hydrocarbon products occurred when doubly labelled vinyls (13C2H3Br. (13C2H3)4Si, or 13C2H4) were added as molecular probes to the hydrogenation of carbon monoxide over rhodium/ceria/silica catalysts (1 atm, 220°C). There was, by contrast, no significant incorporation of 13C1 into any of the organic products; thus cleavage of the C2 probe did not occur. The degree of 13C2 incorporation decreased with increasing molecular mass of the hydrocarbon; this indicates that the probe molecule initiated but did not propagate. A mathematical model based on polymerisation of surface methylenes initiated by a vinyl, propagated by alkenyls and terminated by reaction with a surface hydrogen or by coupling has been developed to explain the 13C2 incorporation data. Under the conditions of the experiments, the relative ability of the probes to initiate is: vinyl bromide (60%)〉tetravinylsilane (30%)〉ethene (15%). Substantial formation of 13C4 products also occurred when vinyl bromide or tetravinylsilane were used as probes; this arises from a dimerisation of the vinyl on the surface, a process which has been modelled in homogeneous systems and also by other workers in studies on single crystal surfaces. There was no significant 13C incorporation into the oxygenates (methanol, ethanol, acetaldehyde); these products are formed by a different path.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 93
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 94
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 95
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 96
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 568-572 
    ISSN: 0947-6539
    Keywords: allylic substrates ; amidinomycin ; asymmetric syntheses ; carbanucleosides ; palladium catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The amino acid derivative in the title represents an important building block for the synthesis of a number of biologically important targets such as the antiviral carbanucleosides and amidinomycin. By using asymmetric palladium-catalyzed desymmetrization of meso-2-ene-1,4-diols, cis-1,4-dibenzoyloxy-2-cyclopentene can be converted to the enantiomerically pure title compound in only four steps. Chemoselective ester reduction allows entry into the domain of carbanucleosides, whereas double-bond reduction provides the precursor for amidinomycin. In an ancillary study, a facile diastereoselective cis-hydroxylation provides aminocyclopentitols, compounds that have proven to be potent glycosidase inhibitors.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 97
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 594-597 
    ISSN: 0947-6539
    Keywords: electron microscopy ; gels ; helices ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, molecular structure, and properties of a new chiral gelforming agent 1 are described. Key structural features in 1 are a γ-alkoxybutyro-lactone tetralin moiety and an angular phenylsulphone unit. The new low molecular weight gelator 1 can reversibly form stable gels in low concentrations (e.g., 1:800 for n-hexane) with isopropanol and a variety of apolar organic solvents. The gels were studied with differential scanning calorimetry and a combination of electron microscopy techniques, which revealed a highly ordered three-dimensional network of entangled fibers. X-ray analysis showed that the aggregation of 1 leads to a helical structure in the solid state. Nonchiral analogues 2 and 3 were unable to initiate gel formation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 98
    ISSN: 0947-6539
    Keywords: gas-phase chemistry ; mass spectrometry ; periodic trends ; peroxides ; transition-metal ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bimolecular gas-phase reactions of d-block transition-metal cations M+ with dimethyl peroxide were screened by means of Fourier transform ion cyclotron resonance mass spectrometry. The rich chemistry can be classified into four types of reactions: i) Oxygen-atom transfer to generate MO+, ii) elimination of radicals, mostly CH3O·, iii) intramolecular redox reaction of dimethyl peroxide to form CH3OH, CH2O and CO, and iv) charge transfer from the metal cation to produce CH3OOCH3+. Some general trends became apparent from this study. For example, the “early” transition metals almost exclusively induce oxygen transfer to generate MO+, in line with the notoriously high oxophilicities of these metals, and electron transfer is only observed for Zn+ and Hg+. Both the radical loss and the disproportionation reaction emerge from a rovibrationally highly excited insertion intermediate (CH3O)2M+, and for the first-row metals the branching ratio of the competing processes seems to be affected by the M+—OR bond strengths as well as the electronic groundstate configurations of M+. For the 4d and 5d cations Ru+—Ag+ and Pt+—Au+, respectively, products resulting from intramolecular redox reactions dominate; this probably reflects the higher propensity of these metal ions to facilitate β-hydrogen atom shifts.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 99
    ISSN: 0947-6539
    Keywords: chemical bonding ; electron localization ; scanning tunnelling microscopy ; surface structures ; tight-binding calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The advantage of computer graphics in the visualization of tight-binding calculations is highlighted in a model study of the reconstruction of the Si(100) surface. Three different surface models - the unreconstructed surface Si(100)-(1 × 1), and symmetric and asymmetric pairing of surface atoms Si(100)-(2 × 1) - are investigated on the basis of density of states (DOS), local (projected) density of states (LDOS) and crystal orbital-overlap population (COOP) analysis. For the visualization of the real-space properties of tight-binding calculations, two- and three-dimensional images of the total (TED) and partial electron densities (PED) are shown. The PED calculated near the Fermi level are compared to densities of HOMOs and LUMOs in molecular systems and used to analyse constant current mode STM images, obtained by applying bias voltages of different sign. They show excellent agreement with STM experiments. The electron-localization function (ELF) has been shown to describe chemical bonds in molecules and solids surprisingly well. Here, the ELF is calculated for surfaces. In order to visualize the shape of the “dangling” surface bonds and bonds connecting surface atoms, two- and three-dimensional representations of the ELF are discussed. Using the reconstruction of the Si(100) surface as an example, we show that combining methods for extracting information from quantum mechanical calculations, such as PED, TED and ELF, leads to a more comprehensive description of the electronic surface structure. With the help of computer graphics, chemical concepts routinely used for describing local properties of molecules can be transferred very effectively to extended systems.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 100
    ISSN: 0044-8249
    Keywords: Antikörper ; Immobilisierung ; Immunsensoren ; Photolithographie ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 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...