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  • 1985-1989  (1,097)
  • 1920-1924
  • 1988  (1,097)
  • Organic Chemistry  (765)
  • Computational Chemistry and Molecular Modeling  (332)
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Material
Years
  • 1985-1989  (1,097)
  • 1920-1924
Year
Keywords
  • 101
    Electronic Resource
    Electronic Resource
    Synthesis, Structure Elucidation, and Pharmacological Evaluation of 5-Methyl-oxymorphone (= 4,5α-epoxy-3,14-dihydroxy-5,17-dimethylmorphinan-6-one) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1801-1804 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of 5-methyl-oxymorphone (3) was accomplished by oxidation of 5-methylthebaine (4) with performic acid, followed by catalytic hydrogenation and cleavage of the 3-MeO group. X-Ray analysis confirmed that the 14-OH group has, like the one in oxymorphone (1), β-orientation. Pharmacological studies in vivo and in vitro showed 3 to possess slightly less opioid agonistic properties than 1.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710721
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  • 102
    Electronic Resource
    Electronic Resource
    Synthese des Flechtenmakrolids (+)-Aspicilin mit Photolactonisierung als SchlüsselreaktionAus den Dissertationen oder Diplomarbeiten von N. H. [1], J. G. [2], U. D. [3], M. E. [4], U.-M. B. [5].Die Essenz dieser Mitteilung ist in Zuschriften [6] sowie in Vortragsreferaten [7] enthalten.In dieser Mitteilung werden folgende Abkürzungen verwendet: BHT: 2,6-Di(tert-butyl)-4-methylphenol, DABCO: 1,4-Diazabicyclo[2.2.2]octan, DBU: 1,8-Diazabicyclo[5.4.0]undec-7-en, DHP: 3,4-Dihydro-2H- pyran, DIBAH: Diisobutylaluminium-hydrid, DMAP: 4-(Dimethylamino)pyridin, MAD: Methylaluminiumbis[2,6-di(tert-butyl)-4-methylphenoxid], MCPBA; m-Chlorperbenzoesäure, MOM: Methoxymethyl, MTPA: α-Methoxy-α-(trifluoromethyl)phenylessigsäure, NBS: N-Bromsuccinimid, NMI: N-Methylimidazol, NOE: ‘nuclear Overhauser enhancement’, PPTS: Pyridinium-p-toluolsulfonat, THP: Tetrahydropyranyl, TMEDA: N,N,N′,N′,-Tetramethylethylendiamin.Sir Derek Barton zum 70. Geburtstag gewidmet (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1719-1794 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of the Lichen Macrolide (+)-Aspicilin Using Photolactonization as a Key Reaction(+)-Aspicilin, obtained from a lichen source of the Black Forest, has been proven to have the absolute configuration depicted by formula la. It is easily built up from phenol (14a), 1,9-nonanediol (13a), and (-)-(S-) methyloxiarane (6) (cf. Scheme 2). The latter building block provides the first stereogenic center C(17). The heterocycle is produced by photolactonization, fairly early during the course of the synthesis. The second stereogenic center is generated diastereoselectively at C(6) in compound 8, conveniently available from photolactone 9a or 9b/9c. Its absolute configuration depends on the kind of reducing agent and is controlled by long-range conformational transmission of chiral information. To explore the cause of stereoselection, 2D-NMR spectroscopy, X-ray structural analysis, and/or computer-aided conformational search followed by energy minimization have been used extensively, revealing the importance of the local conformation of the lactone moiety. Compound 8, on treatment with Yamamoto's reagent, affords pre-target compound 7a almost exclusively. The latter compound, on pyridine-accelerated dihydroxylation with OsO4, gives preferentially (+)-Aspicilin.
    Additional Material: 37 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710719
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  • 103
    Electronic Resource
    Electronic Resource
    Intramolecular Dynamics of Tetranuclear Carbonyliridium Cluster Compounds. Part IIPart I:[4].. Disubstituted complexes with one chelating ligand. Crystal structure of [Ir4(CO)7(μ-CO)3(1,5-cyclooctadiene)] (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1885-1894 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two complexes [Ir4(CO)10(diarsine)] (1) and [Ir4(CO)10(1,5-cyclooctadiene)] (2) bear a bidentate ligand chelating one metal atom of the basal face of the Ir4 tetrahedron. However, they differ in fluxional behaviour as observed by 2D-exchange and variable-temperature 13C-NMR. The CO-site exchange with lowest activation energy proceeds via an unbridged intermediate in 2, whereas that in 1 occurs via a concerted edge-bridging of CO's to an alternative face of the metal core. This difference is apparently related to different ground-state geometries: the basal CO's are symmetrically bridging in 2, whereas two CO's are semi-bridging in 1. The molecular structure of 2 was determined by single crystal X-ray diffractometry. The crystals are orthorhombic, space group Pbca, a = 11.651(4), b = 13.118(3), c = 28.64(1)Å. The idealized molecular symmetry is Cs. The diolefin chelates a basal Ir-atom replacing an axial and a radial CO group on the tetrahedral metal-atom framework.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710807
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  • 104
    Electronic Resource
    Electronic Resource
    Synthesis of New, Unnatural Macrocyclic Trichothecenes: 3-isoverrucarin A ((1″-O)(3→4)abeo-verrucarin A), verrucinol, and verrucene. 46th Communication on verrucarins and roridins45th Communication: [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1895-1903 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new unnatural macrocyclic trichothecene, an analogue of verrucarine A (1), which was named 3-Isoverrucarin A ((1″-O)(3→4)abeo-verrucarin A; 3) was synthesized starting from anguidine (5). The two key reactions were the removal of the 4β-acetoxy group of anguidine (5) by a Barton deoxygenation and the final macrolactonization. During the cyclization procedure, two unexpected new macrocyclic by-products, which were named verrucinol (19) and verrucene (20), were formed. They represent novel types of macrocyclic trichothecenes, the macrolidic moiety of verrucene (20) consisting only of the (Z,E)-muconic-acid residue. The formation of the analogous macrolide 26 of verrucene (20) was not possible, probably because the ring strain is too strong.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710808
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  • 105
    Electronic Resource
    Electronic Resource
    The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene, syntheses, photolyses, X-ray-structure analysis, and PE spectra (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1937-1965 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The propensity of the N=N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1-3, no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray (1: d = 2.71 Å, ω = 129°) and PE measurements (1: I1 = 8.00, I2 = 9.05 eV; 2; I1 = 8.00, I2 = 9.25eV). The steric/stereoelectronic demands for the participation of the N=N bond in pericyclic reactions are clearly more stringent than those for the C=C bond.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710813
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  • 106
    Electronic Resource
    Electronic Resource
    Thioalkylation of Meldrum's Acid: Protected alkylidene derivatives of isopropylidene malonate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1974-1982 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thioalkylated Meldrum's acid is easily by treatment of Meldrum's acid with an aldehyde and thiophenol in the presence of catalytical amounts of piperidinium acetate (→1-6, Table 1). The adducts 1-6 are crystalline, stable compounds and they can be caused to react directly with nucleophiles and dienes (see 3→7-12, Scheme 1). The regeneration of the parent olefin is effected thereby by simply dissolving the adduct under neutral or basic conditions. Extension of this method to thiocarboxylic acids allowed the preparation of the corresponding formaldehyde derivatives 13 and 15 (Table 3).
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710816
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  • 107
    Electronic Resource
    Electronic Resource
    Synthese von Triafulven-Vorstufen aus trisubstituierten Cyclopropanen54. Mitt. über Fulvene, Fulvalene, 53. Mitt.: [1]. Kurzmitt.: [2] [3]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2026-2033 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Triafulvene-Precursors from Trisubstituted CyclopropanesTrisubstituted cyclopropanes 5a-f are prepared by carbene addition to the appropriate olefins. While 5a (Y = OAc) and 5c (Y = Cl) rearrange in the presence of BuLi, 5d (Y = SPh) is stable enough to allow the envisaged sequence for triafulvene (Scheme 2) : halogen-Li exchange, followed by methylation of 6d, gives 7d in a 93% yield; after base-induced elimination of HBr from 7d, the key precursor 1-methylene-2-(phenylthio)cyclopropane (9, 70% yield) is isolated. Compound 9 is transformed into the corresponding sulfoxide 10 (83%), sulfone 11 (80%), and sulfonium fluoroborate 12 (95% yield) by subsequent oxidation and methylation, respectively. Some 1H-NMR results of cyclopropanes 5a-f and 7d as well as of methylidene-cyclopropanes 9-11 are discussed.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710820
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  • 108
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Mikroorganismen. 251. Mitteilung250. Mitteilung: [1].. Die Esmeraldine A und B, tief grüne Farbstoffe aus Streptomyces antibioticus, Stamm Tü 2706 (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2058-2070 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Esmeraldines A and B, Green Pigments from Streptomyces antibioticus, Strain Tü 2706From a strain of Sterptomyces antibioticus, Tü 2706, two dark green substances, the esmeraldines A and B, 4 and 3, respectively, were isolated. The structural elucidation was carried out by spectroscopic comparison with some simpler phenazines obtained from the same organism, saphenamycin (1) and related compounds, and by a series of chemical transformations. Esmeraldin B (3) is the 6-methylsalicylic acid ester, and esmeraldin A (4) a mixture of higher saturated and unsaturated fatty acid esters of esmeraldic acid. The latter is a heterocyclic compound with seven rings and four N-atoms, formally derived by condensation of two phenazine residues of the saphenic acid family. The esmeraldins are mixtures are of diastereoisomers.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710824
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  • 109
    Electronic Resource
    Electronic Resource
    Mitteilungen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2173-2174 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710828
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  • 110
    Electronic Resource
    Electronic Resource
    Bathophenanthroline-ruthenium(II) complexes as non-radioactive labels for oligonucleotides which can be measured by time-resolved fluorescence techniques (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2085-2099 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The specific attachment of bathophenanthroline-ruthenium(II) complexes as non-radioactive label molecules to synthetically 5′-NH2-modified oligonucleotides is described. After excitation by light pulses, the fluorescence of these labels can be measured by a time-resolved mode woth high sensitivity. No quenching takes place due to coupling of the Ru complexes to the DNA. Ru-complex-labelled oligonucleotides still hybridize specifically to complementary DNA sequences, and no quenching is observed in the course of the hybridization process.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710826
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  • 111
    Electronic Resource
    Electronic Resource
    Crystal Structure and Electron-Density Distribution of Two [1.1.1] Propellane Derivatives at 81 K (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 2100-2110 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular structure and electron-density distribution of two [1.1.1]propellane derivatives have been determined from accurate single-crystal X-ray diffraction measurements at 81 K. The crystals of these highly reactive compounds (both are liquid at room temperature) were grown directly on the X-ray diffractometer at ca. 208 and 228 K, respectively. Both compounds crystallize in the space group P21/c with one molecule in the asymmetric unit. The symmetry of the propellane C-atom skeleton is close to D3h for both molecules. The distances between the two bridgehead C-atoms are 1.587 and 1.585 Å, and the mean lengths of the propellane side bonds are 1.525 and 1.528 Å, respectively. The deformation density peaks of the propellane side bonds (ca. 0.25 e/Å3) lie somewhat outside the internuclear connection lines and so correspond to ‘bent bonds’ as expected. On the other hand, the difference electron density between the bridgehead nuclei is slightly negative in both molecules. An interesting feature, observed in these difference maps, is presence of a diffuse, positive difference density at each inverted C-atom, outside the bridgehead bond, a probable site of electrophilic attack.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710827
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  • 112
    Electronic Resource
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    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 585-585 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330614
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  • 113
    Electronic Resource
    Electronic Resource
    Theoretical studies on conformational preferences of model modified nucleic acid base N6-(N-alanylcarbonyl) adenineNCL Communication No. 4069. (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 37-46 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational preferences of model modified nucleic acid base N6-(N-alanylcarbonyl) adenine, ac6Ade, have been investigated using the quantum chemical PCILO (perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining the various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually.The preferred molecular structure is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The observed crystal structure conformations for the naturally occurring, anticodon adjacent, threonyl analogs, tc6Ade, correspond to the predicted most stable conformation for the model modified base ac6Ade. Three stable, low energy conformations differing in the orientations of the carboxyl group and the amino acid side chain are predicted within 1 kcal/mol of the most stable structure. The possible bifurcated hydrogen bonding of N(11)H with N(1) and either of the carboxyl oxygens is of minor significance.The indicated orientational flexibility for the carboxyl group and the amino acid side chain may enable convenient probing of the molecular environment, in the vicinity of the anticodon in tRNA, by the amino acid substituent, with only modest changes in energy stabilization.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340106
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  • 114
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    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 89-90 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340111
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  • 115
    Electronic Resource
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    A regular periodic table of the elements and its quantum mechanical requirement (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 107-119 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By using the n + (1/2)l filling rule of the atomic Aufbau principle, where n is the principal quantum number and l is the azimuthal quantum number, a new periodic table is presented, its periods having, in order, 8, 18, 18, 32, 42, 50, … elements. The mentioned rule is proposed instead of the n + l rule (or Madelung's rule) which constitutes the quantum mechanical basis of the current periodic table and predicts periods having, in order, 2, 8, 8, 18, 18, 32, 32, 50, … elements. The new periodic table is called “regular” because its groups are formed according to a single rule (namely, the first elements of each period are placed in the same order as the elements of the preceding period), in contrast with the current periodic table, where no simple rule can be applied for the same purpose. The most characteristic feature of the regular periodic table is the fact that its groups are also related in a periodic manner.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340204
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  • 116
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    Control over theoretical descriptions of atoms and molecules. An information theoretic approach to the automatic classification and systematic improvement of approximate wave functions (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 185-190 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A rigorous approach to the study of the quality of theoretical descriptions of atoms and molecules is proposed. Theoretical descriptions, i.e., collections of atomic or molecular properties obtained via quantum chemical methods, are associated with information quantities defined with respect to reference theoretical or experimental data. In this way the comparison of two theoretical descriptions is reduced to the comparison of the respective information quantities. An increase in information is interpreted as improvement of the theoretical description. The aforementioned approach should be useful in problems related to classifications and systematic improvements of approximate wave functions and consequently for comparing the performance of quantum chemical methods in calculations of atomic and molecular properties. This approach should also constitute a powerful tool for the construction of suitable basis sets for use in calculations of atomic and molecular properties.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340209
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  • 117
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    Spin and charge densities from Hiller-Sucher-Feinberg identities. Test calculations for He, B, C, N, O, and F atoms and H2O, N2, and CH3 molecules (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 195-197 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340212
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  • 118
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    Fifth-order constant denominator perturbation therory within a localized bond model: Contributions from single and double excitations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 497-527 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Fifth-order constant denominator perturbation treatment of all single and double excitations occuring in the third-order perturbation wave function is presented for the perturbation configuration interaction using localized orbitals (PCILO) method. Contributions from triple and quadruple excitations which decay back to singles and doubles at third order are automatically included in this theory. This method is computationally very fast, with an execution speed proportional to N3, Where N is the number of orbitals present. A [2,1] Padé approximate involving only singles and doubles contributions through to fifth order is shown to be remarkably accurate.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330604
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  • 119
    Electronic Resource
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    Hall transformation of exp( - r): Correction of the results (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 563-566 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Owing to an error in his determination of the repulsion integral and the kinetic energy. Hall's results [1] for the ground state of atomic two-electron systems are wrong. Here these results have been corrected. For Z ≤ 5, the results have been obtained by determining the pertinent integrals numerically: but for Z ≥ 5, these can be found sufficiently accurately from Z expansions.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330608
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  • 120
    Electronic Resource
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    Ab-initio calculation of resonance states of H2O (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 567-576 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a dissociation attachment experiment of water, three peaks were observed at 7,9, and 12 eV. The origin of the third peak has been believed to be 2B2. However, the calculated energy of this state is 0.6 eV higher than the experimental value. This discrepancy is quite large compared with the case of the lower two peaks. In this study we propose new candidates for resonant states responsible for the third peak. The configurations considered are (3a1)-1(3pa1)2, (3a1)-1(3pb1)2, (3a1)-1(3pb2)2, (3a1)-1(3pa1)1(3pb1)1, (3a1)-1(3pb2)1(3pa1)1, and (3a1)-1(3pb2)1(3pb1)1 which have the parent state (3a1)-1(3pa1)1, (3a1)-1(3pb1)1, or (3a1)-1(3pb2)1. The energy levels arising from these configurations are calculated by a method of configuration interaction. A Few resonance states, which could be responsible for the third peak, are found. New decay process of these states are proposed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330609
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  • 121
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    The sequential product of geminals and the ground states of some atoms (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 9-14 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By means of the SPG function which is associated with an extreme point of the set of N-representable second-order reduced density matrices, an attempt is made to perform the calculations of the ground states of some atoms with four electrons such as Be. The results show that the SPG function is as suitable as the well-known AGP function for approximating the ground states of atoms and molecules.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340103
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    A sequential product of geminals and its applications (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 15-23 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, an SPG function, which is associated with an extreme point of the set of N-representable second-order reduced density matrices, is used to perform the calculation of the ground state energy of LiH with the variation of internuclear separation. The result of our calculation essentially is in accordance with that of AGP function.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340104
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  • 123
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    The concept of the topological atom within the MO-LCAO approach. II. On the nature of the nephelauxetic effect (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-8 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new MO-LCAO description of the nephelauxetic effect is proposed based on the concept of the topological atom and on the method of reduced density matrices. This approach allows one to overcome some conceptual difficulties of ligand-field theory and to derive effective parameters of d-d electron repulsion of a bound transition-metal in a proper way. The two ligand-field mechanisms of the nephelauxetic effect - the central field covalency and the symmetry-restricted covalency - are clarified and generalized. In addition, a new factor, important for the nephelauxetic effect is found: its size-dependence on the region of the topological atom.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340102
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    A Crystal Orbital approach for two- and three-dimensional solids on the basis of CNDO/INDO Hamiltonians. Basis equations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 47-71 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Hartree-Fock (HF) self-consistent field (SCF) crystal orbital (CO) formalism for two- and three-dimensional (2D/3D) solids on the basis of semiempirical CNDO/INDO (complete neglect of differential overlap; intermediate neglect of differential overlap) Hamiltonians is presented. The employed SCF variants allow for the treatment of atomic species up to bromine under the inclusion of the first (i.e., 3d) transition metal series. Band structure investigations of 2D and 3D materials containing more than 30 atoms per unit cell are feasible by the present SCF HF CO formalism. The theoretical background of the computational scheme is given in this contribution. Special emphasis is placed on physically reliable truncation criteria for the lattice sums, the adaptation of the crystal symmetry in k space, as well as the suitable choice of domains in Brillouin zone (BZ) integrations required in the determination of charge-density matrices. The capability and limitations of the semiempirical SCF HF CO approach is demonstrated for some simpler solids by comparing the present computational results with those of ab initio CO schemes as well as conventional numerical methods in soid-state theory. The employed model solids are graphite and BN (2D and 3D networks for both solids) as well as diamond, silicon, germanium, and TiS2.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340107
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  • 125
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    Long distance electron transfer (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-22 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum mechanical models to treat long distance electron transfer are being developed. The model is based on the theory of R.A. Marcus. Our contribution is in the calculation of the electron coupling factor k. Estimations of the latter number, as well as the bond and solvent relaxation energies, λi and λo, respectively, are necessary to be able to calculate the rate constant for a reaction of the conductivity in an electric field. k may be approximately calculated from orbital energy differences at avoided crossings between orbitals localized in different parts of the system. A novel spectroscopic NDO method is suggested in which one may include any atom of the periodic table. Another problem discussed is the inclusion of electronic relaxation effects of the solvent or protein in the calculation. Applications are made to systems where metal ions are connected by organic bridges of different kinds such as dipyridine with coplanar and perpendicular pyridyl groups. As expected the electronic factor depends strongly on the conformation of the bridge. A strong conformational dependence is also obtained for a saturated bridge of the type NH2 · (CH2)n · NH2. In another study we use an α helix as a bridge between two metal ions. If one glycine in this α-helix is substituted by phenylalanine the electronic factor increases by factors of 1.5-10. It is suggested, however, that larger enhancement factors are possible if an aromatic group is positioned in a favorable way. The CNDO/S method is used to study the charge separation process in a bichromophoric molecule and in the reaction center (RC) of Rhodopseudomonas viridis. In those cases where the electronic coupling is large enough for the charge transfer states to be seen in the spectrum, the calculated results agree well with the experimental ones, but suggest a novel assignment. The CNDO/S results verify that electron transfer is possible through saturated spacers. In the special pair of RC the S1 state is calculated at approximately the correct position. Like the ground state, it has a delocalized character.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340704
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    Electrostatic interactions and conformation of some thromboxane antagonists (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 67-84 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A class of thromboxane antagonists exists where the prostaglandin side chain containing the C16 hydroxyl moiety is replaced by a phenyl ring, and the bridged six-membered pyranose moiety by cyclohexane, pyranose and dioxane ring systems. Analysis of antagonist potency data in terms of a binding constant model previously used for membrane bound receptor-drug interactions shows that the major patterns of antagonist potency are governed as much by axial/equatorial conformer preference of the phenyl moiety and its orientation as by electrostatic effects of the aliphatic ring oxygen atoms. The conformational restriction of the two substituted side chains of the σ-bonded 6-membered ring is shown to be a primary requirement for binding to thromboxane receptors, and a quantitative separation of electrostatic and conformational components in the potency data is attempted.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340708
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    An ab initio molecular orbital study of hydrogen bonding and ion-molecule association in model systems for DNA bases (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 119-135 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations have been performed to investigate hydrogen bonding and ion-molecule association in complexes of H2O with the neutral, protonated, and Li+ complexes of N-formylformaldehyde and N-formylformamidine. In the complexes with the neutral bases, H2O assumes an in-plane bridging position in the amide and amidine regions. The most stable complex is the bridging N-formylformamidine-H2O complex in the amidine region, which has an MP2/6-31 + G(d,p) binding energy of -9 kcal/mol. Hydrogen bonded complexes of H2O with the oxygen-protonated bases have open structures with the protonated bases as proton donors, and binding energies ranging from -16 to -24 kcal/mol. Nitrogen protonation of N-formylformamidine leads to an equilibrium chelated hydrogen bonded structure with a stabilization energy of -21 kcal/mol. When Li+ associates with these bases at a carbonyl oxygen, hydrogen-bonded bridging structures with H2O reappear, and wobble complexes exist in the amide and amidine regions of N-formylformaldehyde and N-formylformamidine. These complexes have binding energies of -13 to -14 kcal/mol. However, the most stable comples has H2O directly bonded to Li+, with an MP2 binding energy of -30 kcal/mol. No hydrogen bonded structures of H2O with N-formylformamidine exist in the amide region when Li+ associates with this base at the C=N group. Hydrogen bond energies computed at the single-determinant Hartree-Fock level with the 6-31G(d) basis set approximate correlated MP2/6-31 + G(d, p) energies to within 1 kcal/mol for all of the neutral and charged complexes. However, when H2O is bonded to Li+, HF6-31G(d) association energies overestimate MP2/6-31 + G(d, p) energies by 3 kcal/mol.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340712
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    Dependence of MO shapes on a continuous measure of delocalization (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-13 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Whereas localization of orbitals has long been a tool for a semiclassical interpretation of chemical properties, it is in fact electron delocalization that is a fundamental property of quantum mechanical molecules. A mathematically well-defined measure is suggested for the degree of delocalization of molecular orbitals. It is shown that an orbital set of maximum delocalization exists for which the degree of delocalization depends on the charge distribution of the molecule. Hartree-Fock canonical orbitals are definitely more localized than the most uniformaly distributed MO's giving an equivalent description of the molecule. The changes in the geometrical shape of molecular orbitals are studied passing (quasi-) continuously from the strongly localized description towards the most delocalized picture. In the case of charge-inhomogeneities even the most delocalized orbitals remain rather compact. The degree of maximum delocalization may be correlated with chemical properties such as reactivity. The shape distortion of MO's under the perturbing effect of other ions and small molecules is investigated in several examples.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340804
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    Density and density matrix from optimized linearly independent product basis functions for Be (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 43-49 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The density matrix was computed from the density using basis orbitals which form linearly independent products (LIP). Calculations were performed on the Be atom using LIP bases containing several of the natural spin orbitals from an accurate nonrelativistic 650-term configuration interaction (CI) wavefunction. Calculations were also performed using a basis set of 6 s-type orbitals optimized so that the lowest eigenvalue, d1, of the overlap matrix of products is maximized and the energy of a small CI wavefunction is minimized. The value of d1 in the optimized basis is 1 × 10-7. The density and the potential energy obtained from the 650-term CI wavefunction were accurately reproduced by the density matrix expressed in the optimized LIP basis, but the kinetic energy was somewhat less accurate.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340809
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    Geometry optimization using local-density functional methods: Numerical aspects (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 77-84 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The need to perform a numerical integration of the exchange-correlation functional because of its non-analyticity severely complicates the accurate application of local-density functional methods to molecules and clusters. The optimal choice of grid points for this integration and the estimation of the error made by the choice are subtle considerations. In particular, because the position and/or weighting of each grid point must change when the nuclear positions change, these errors are most noticeable when different geometries are compared. We have determined a method of grid point selection and weighting that reduces these errors. We have also determined a simple method of estimating the extent of the error made in the particular density of points used for the grid. These results are illustrated for a selection of small molecules.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340813
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    Topological electronic rules for polycyclic hydrocarbons - quantum chemical deductions directly from structural formulas (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 143-147 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All bicyclo[p.q.0] conjugated hydrocarbons are found to fall into ten homolog classes each characterized by the numbers of nonbonding, bonding, and antibonding molecular-orbitals of its first prototype and by the prototype itself. The energy level patterns are obtained by the new “structural covariance” pictorial rules directly from structural formulas. The HOMO-LUMO types, aromaticity or three types of nonaromatic behavior, and reactivities towards nucleophiles or electrophiles thereby also result.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340818
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    Calculation of harmonic frequencies and harmonic force fields by the hartree-fock-slater method (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 173-181 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results are presented from Hartree-Fock-Slater (HFS) calculations on harmonic frequencies and force constants of H2O, H2S, NH3, PH3, CH4, SiH4, and C2H4. Both frequencies and force constants were calculated by a numerical (finite difference) differentiation of analytical energy gradients. It is shown by a comparison with experimental data and results from ab initio Hartree-Fock (HF) calculations that the HFS-method provides harmonic frequencies and force constants in at least as good agreement with experiment as the HF-scheme.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340821
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    A progress report on the status of the COLUMBUS MRCI program system (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 149-165 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The COLUMBUS program system is a collection of Fortran programs for performing general multireference single- and double-excitation configuration interaction (MRSDCI) wave function optimization based on the graphical unitary group approach. The program system also includes integral generation, SCF and MCSCF orbital optimization, integral transformation, and wave function analysis programs. The original program system was written in 1980 to 1981. Since that time, it has evolved into one of the most popular MRSDCI program systems used in the computational chemistry community. The discussion of this evolution will include the exploitation of efficient matrix-matrix and matrix-vector product computational kernels, the use of generally contracted symmetry-adapted orbital basis sets, general Hamiltonian diagonalization procedures, energy-based internal walk selection, flexible DRT specification, improved coupling-coefficient evaluation methods, coupled-pair functional and multireference CPF capabilities, and density matrix construction. The numerous versions of the program system that are maintained at different sites and on different computers are now in the process of being merged. The source code for this combined version will be made available to the computational chemistry community. The source code for a specific computer may be generated from the source code for another computer by a single pass through a simple filter utility that is included with the program system. The directly supported computers will initially include various models of VAX, Cray, FPS, IBM, CDC, and ETA machines with the addition of other machines shortly thereafter. The ongoing developments of the COLUMBUS system that are discussed include a new method for computing analytic energy gradients for MRSDCI wave functions. This effective-density-matrix based method avoids the “coupled perturbed MCSCF” solutions for each coordinate direction, avoids the transformation of any derivative-integral quantities from the AO to the MO basis, avoids the transformation of the coupling coefficients from the MO to the AO basis, allows a subset of the MCSCF doubly occupied orbitals to be frozen in the CI wave function, and allows the MRSDCI wave function to be generated from general reference CSFs that are not necessarily related to the MCSCF expansion CSFs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340819
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    Theoretical study of the geometry of Mn5 (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 231-236 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometry of Mn5 in rare gas matrices has been proposed to be a planar pentagon with 25 unpaired electrons. Simple unrestricted Hartree-Fock (UHF) calculations have been carried out using a basis of STO-6G for 1s, 2s, and 2p orbitals with STO-4G for 3s, 3p, 3d, 4s, and 4p in the HONDO5 program. The structure is optimized at the UHF level using the analytic gradient formalism for a planar pentagon. Binding energies and spinmixing are given for the optimized structure.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340827
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    Molecular hardness and softness parameters and their use in chemistry (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 349-366 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The semiempirical Atoms-in-a-Molecule (AIM) hardness matrix, η, is defined, using the usual finite difference formula, ηii = Ii - Ai, for the diagonal AIM hardness and the Ohno formula, ηij = 1/(a2 + R2ij)1/2, for the off-diagonal AIM hardness. The Ohno formula is shown to exhibit the correct asymptotic behavior and satisfies the relevant stability criterion. The normal displacements in the AIM electron populations are examined for pyrrole and N-methyl pyrrole, and their relation to the polarization channels is briefly discussed. The new AIM hardness matrix is also tested by comparing the predicted global hardnesses with the corresponding experimental finite difference data for selected diatomics and triatomics. Finally implications of the hardness combination rules are examined and the corresponding softness combination rules are used to calculate the regional and global softnesses of selected molecules. We examine how the regional softnesses reflect known trends in selectivity of protonation of five membered heterocycles, and comment on the signs of the AIM fukui function and the Hard-Soft-Acids-and-Bases principle.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340840
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    Modified breit-pauli hamiltonian suitable for variational calculations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 425-430 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Breit-Pauli type Hamiltonian with an effective positive term in substitution of the Darwin term is proposed for variational calculations. The Hamiltonian is bounded from below and does not exhibit variational collapse. Calculations on one electron atoms for the ground state, 2pl/2 and 2p3/2 states are presented. The results essentially coincide with those obtained from first order perturbation theory.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340845
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    Titanium in large silicon clusters (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 297-308 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of molecular ab initio methods to investigate the electronic structure of localized impurities in semiconductors requires the study of the convergence of the results with increasing cluster size. Here we compare results for interstitial Ti in silicon, obtained with clusters of increasing size: TiSi10H16, TiSi30H40, and TiSi66H64. These clusters contain one, two, or three shells of silicon atoms, respectively, centered around Ti at a Td interstitial site. The hydrogen atoms serve as saturators of the dangling bonds. The Si core electrons are replaced by an effective potential. The calculations are based on open shell RHF theory and limited CI extensions. The charge distribution in the central part of the three clusters is very similar. In the clusters the partially occupied orbitals are much more delocalized than the 3d orbitals in the free ions. The total impurity-induced electronic charge, however, is quite localized, due to the compensating response of the Si closed shell density. Ionization of the impurity also causes a compensating response of the Si closed shells: only about 10% of the density difference is in the impurity region and the major part is behind the outermost shell of Si atoms. Transition metal associated (3d-like) excitation energies are not very dependent on the cluster size, and the relative ordering of the lowest lying states remains unchanged. Impurity associated ionization energies decrease considerably due to the extra relaxation offered by the additional shells of Si atoms. Our results indicate that a reliable description of interstitial transition metals in silicon can be provided by calculations on reasonably small clusters: Si30H40 is sufficiently large.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340834
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    Theoretical kinetic and thermodynamic study on the disilene-silylsilylene isomerization (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 343-347 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The titled isomerization has been studied at the HF/3-21G level. The changes in thermodynamic functions, equilibrium constant K(T), conversion efficiency C(T), and the rate constant k(T) for the isomerization have been calculated using our energies of the reactant (R), transition state (TS), and product (P), their harmonic vibrational frequencies, and the classical and corrected barrier (by vibrational zero-point energies). In the range of temperature, 300-1200K, ΔH 〈 0, ΔS 〉 0 and ΔG 〈 0; i.e., it is exothermic, increasing in the entropy, and spontaneous reaction. ΔS≠ 〈 0, log A is about 12.0 ±0.15 (s-1), but the k(T) is from 2.627 × 10(-33) to 6.933 × 10(8) (5-1); i.e., it passes through a tight TS, the A factor changes little, but the rate constant varies rapidly with the temperature. These results agree with the fact that the isomerization occurs readily at high temperature. Furthermore, Newman's mechanism, 2SiH2 → (H2SiSiH2)* → (HSiSiH3)* → Si2H2 + H2, is supported. Similarly, the isomerization, HDSiSiH2 → HSiSiDH2, is also studied.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340839
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    Iteration of the many-particle schrödinger equation in momentum space (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 437-444 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A generalization of the Fourier convolution theorem is used to iterate the many-particle Schrödinger equation in momentum space. The method is applied using hyperspherical coordinates, with many-dimensional hydrogenlike wave functions as the starting point for iteration. The problem of angular integration is converted into a problem of differentiation by means of the theory of harmonic polynomials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340847
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    Relativistic CASSCF/CI calculations: Applications to transition metal dihydrides (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 465-476 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete active space MCSCF (multi-configuration self-consistent field) scheme (CASSCF) using relativistic effective potentials followed by configuration interaction and relativistic CI calculations provides a very good description of the electronic states and potential energy surfaces of transition metal dihydrides. Such calculations are of considerable value not only in our understanding of the transition metal-hydrogen bonding but also in the prediction of the barrier to insert the metal atom into the H2 bond. All-electron CASSCF/CI calculations are carried out on twelve electronic states of CoH2. Comparable RECP-CASSCF/CI calculations are also carried out to show that the RECP-CASSCF/CI calculations provide an accurate method for the investigation of transition metal compounds. The general method of RECP-CASSCF/CI calculations for molecules containing heavy atoms is described. The calculations on CoH2 are compared with similar calculations on ScH2, YH2, PtH2, and PdH2. A critical comparison of all these transition metal hydrides reveals that in general the low-spin excited metal atom inserts into H2 spontaneously while the high spin ground state atom has to surmount a large barrier.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340850
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  • 141
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    The nonabelian two-dimensional algebra and the franck-condon integral (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 503-505 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two mapping operators are used to relate the eigenstates of two distorted and displaced oscillators. It is found that these operators satisfy a nonabelian two-dimensional algebra. We exemplify the method by calculating the Franck-Condon integral for the case of two harmonic oscillator wells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340855
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  • 142
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    Use of quantum mechanical models in studies of reaction mechanisms (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 557-566 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problems involved in determining the mechanisms of reactions by quantum mechanical calculations are discussed. Various precautions must be taken if the results of any calculation are to be chemically meaningful. Ab initio studies of reactions must also be carried out at a high level, using large basis sets and allowing for electron correlation. Such calculations are usually restricted to the simplest example of a reaction, which is often untypical. More information can usually be obtained at far less cost through AM1 calculations for a number of examples of a reaction for which experimental data are available. These points are illustrated by recent studies of the Cope rearrangement.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340860
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  • 143
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    Symbolic computation in quantum mechanics. Several simple examples (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 537-548 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this article is to illustrate the use of symbolic computation in solving some problems in quantum theory. Emphasis will be given to the possibility of manipulating expressions symbolically and to the interface of numerical and algebraic languages. The illustrate the use of the scientific computation language Maple as a research tool, we present our work on lower energy bounds for anharmonic oscillators and on the spherical Zeeman effect. Another example consists in the perturbation calculations of the N-dimensional hydrogen atom, keeping the quantum labels in general form. Further, we describe the interface of Maple, Fortran, and the typesetting language, Troff. The basic feature is illustrated on the application of the inner projection technique and of the method of intermediate Hamiltonians on the benzene molecule as well as on the geminal approach to the butadiene molecule; the main calculations were first done in Maple and then transferred into Fortran's notation so that Fortran subroutines could be used. Finally, the results either in Maple or in Fortran can be transferred to a Troff file.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340858
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  • 144
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    Simple models for describing the fragmentation behavior of multiply charged cations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 567-573 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potential energy curve describing the fragmentation of a diatomic dication AB2+ is considered as arising from an avoided crossing between an attractive diabatic curve (correlating with A2+ + B) and a repulsive diabatic curve (correlating with A+ + B+). The simplest avoided-crossing (AC) model neglects diabatic coupling and polarization and leads to useful predictions of the transition structure bond length (rTS) and the kinetic energy released (T) in fragmentations of dicationic systems in which the difference (Δ1) between the ionization energies of A+ and B is small. When Δ1 is not small, it is necessary to include diabatic coupling and polarization in the treatment. The resultant ACDCP (avoided crossing with diabatic coupling and polarization) model provides very satisfactory estimates of rTS and T for both small and large Δ1. Its implementation requires only atomic ionization energy and polarizability data and comes at virtually no computational cost. Both the AC and ACDCP models are readily generalized to fragmentations of more highly charged cations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340861
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  • 145
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    Spatial correlation of electrons in metals (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 655-664 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of electron-electron repulsions is assessed, primarily in the expanded fluid alkali metals, by confronting experimental data on these systems with the predictions of theory. This is usefully divided into two types of approach: (i)full inclusion of the long-range Coulomb interaction e2/rij between electrons i and j, but perturbative treatment of electron-ion interaction and(ii)the simplified on-site interaction described by the Hubbard U.The main conclusion is that both electron-ion and electron-electron correlations are of major importance in the expanded fluid alkali metals, and especially in Cs. The momentum distribution of the conduction electrons is changed in a very important quantitative way from the predictions of the jellium model at the same density by the electron-ion interaction. This leads to a metal-insulator transition at a much higher electron density than the jellium prediction. The relevance of this conclusion to crystalline alkalis is finally referred to.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340867
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  • 146
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    Electrostatic potential maps of flavone acetic acids: A new class of antitumor drugs (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 697-705 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete geometry optimizations have been carried out with the AM1 method on flavone acetic acid and several of its derivatives. Molecular electrostatic potential maps have been used to predict new com.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340870
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  • 147
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    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 741-741 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340876
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  • 148
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    Masthead (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340101
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  • 149
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    A spin-free form of valence bond theory (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 25-36 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Classical valence bond theory is recast in a spin-free form which provides a practicable route to ab initio calculations of molecular electronic structure. The approach is simple and direct and requires only efficient algorithms for the generation and processing of permutations and the handling of Rumer diagrams: it makes modest demands on computing power and pilot calculations have indeed been performed entirely within the fast memory of a personal computer, which should be sufficient for dealing with systems possessing up to 10 electrons outside a closed shell. Simple applications confirm the conclusion of Cooper et al. [1] that, by using strongly overlapping orbitals, a small number of classical (nonpolar) structures can give results close to those obtained in a “full CI” calculation.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340105
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  • 150
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    The role of hydrophobicity in the Ames test. The correlation of the mutagenicity of nitropolycyclic hydrocarbons with partition coefficients and molecular orbital indices (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 91-101 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A set of 20 nitropolycyclic aromatic hydrocarbons, whose mutagenicity has been determined in the Ames test, has been studied using octanol-water partition coefficients (P) as a measure of relative hydrophobicity and molecular orbital energies to account for variation in their electronic characteristics. A good structure-activity relationship was found using log P and ∊LUMO. The latter were taken from the results of ab initio calculations performed by Maynard, Pedersen, Posner, and McKinney [7] and were also calculated by the MNDO method. The dependence of mutagenicity on hydrophobicity was found to be similar to that observed for triazenes [2]. ∊LUMO values calculated by MNDO and STO-3G were found to be strongly correlated, and the role of hydrophobicity in correlating mutagenicity was not significantly affected by the molecular orbital model employed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340202
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  • 151
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    Molecular conformations and molecular shape: A discrete characterization of continua of van der Waals surfaces (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 517-526 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A characterization of molecular model surfaces is proposed. It is based on a graph associated with the van der Waals surface, defined by the detailed information on the interpenetration of van der Waals spheres of the constituent atoms. This “van der Waals graph” describes the three-dimensional body of the molecule, and it does not coincide in general with the less informative bond graph obtainable from the molecular skeleton.The description in terms of the graph reveals clearly the changes in molecular shape induced by conformational rearrangements. The nuclear configurations can be classified by the graph associated with the molecular surface, and the graph-theoretical analysis provides a rigorous partitioning of the configurational space based on shape properties.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340605
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  • 152
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    The use of symmetry in reciprocal space integrations. Asymmetric units and weighting factors for numerical integration procedures in any crystal symmetry (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 571-594 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic collection of spatial domains for reciprocal space integrations is derived for all possible crystal symmetries. This set can be used as a simpler alternative to the conventional Brillouin zones. The analysis is restricted to integrations where the function in the integrand satisfies inversion symmetry in k space. In this case only 24 different spatial domains have to be defined in order to allow for k space integrations in the 230 different crystal symmetries. A graphic representation of the asymmetric unit for each of the 24 integration domains is given. Special positions and the associated weighting factors required for numerical integrations in theoretical solid-state approaches are tabulated.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340609
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  • 153
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    Thermodynamic calculations on biological molecules (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 221-234 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of free-energy simulation methods to the calculation of thermodynamic properties for biologically relevant processes will be presented. Attention will be given to the usefulness of thermodynamic methods to explore the accuracy of empirical energy functions. Calculations of aqueous hydration and binding thermodynamics for drug molecules (trimethoprim and other related compounds) to biological targets (the enzyme dihydrofolate reductase) will be presented. In these applications we will discuss differences in “binding modes” for different drugs and the ability of thermodynamic methods to predict these changes. Finally, comments will be made regarding the free energy derivative methods and coordinate-coupled free energy calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340720
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  • 154
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    A rational selection of graph-theoretical indices in the QSAR (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 267-285 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we have addressed an important problem: how to develop a strategy for identification of the topological indices which are most important in establishing a model for structure-activity analysis. In particular we consider a rational selection of graph theoretical (topological) indices in QSAR. The approach is illustrated by the study of the toxicity of ethers on mice. The indices examined include the connectivity indices based on adjacency matrix, the conceptually related graph distance indices, and an information theoretic index based on partitioning of electrons in various domains. We have outlined the similarities and differences and discuss advantages and limitations among different approaches. Our emphasis is on the problem how to select in a rational way appropriate graph-theoretical descriptors and how to introduce higher “corrections” in order to improve derived correlation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340724
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  • 155
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    Masthead (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710101
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  • 156
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    Synthesis and Reactions of Optically Active 1,3-Diols (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 47-56 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ‘syn’-1,3-diols 3,4 and 5 with a C7, C6, and C5 chain, respectively, were synthesized from methyl hydrogen 3-hydroxyglutarate (2; Schemes 1 and 2). The latter is available in (R)- and (S)-configuration. Octyl (3R)-4-chloro-3-hydroxybutanoate (17) is an alternative starting material for the preparation of 5 (Scheme 3.) The epoxide 20, derived from 5 in a one-pot reaction, is a versatile synthon, which selectively reacts with a great number of nucleophiles (Scheme 4).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710106
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  • 157
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    Dendryphiellin A, the First Fungal Trinor-eremophilane. Isolation from the marine deuteromycete Dendryphiella salina (SUTHERLAND) PUGHet NICOT (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 57-61 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel metabolite dendryphiellin A ( = (+)-(1R,2S,8aR)- 1,2,6,7,8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*, 2E,4E)-8-hydroxy-6-methylocta-2,4-dienoate; (+)-1) is isolated from cultures of the marine deuteromycete Dendryphiella salina. There is no precedent in fungi for trinor-eremophilanes or for branched C9 carboxylic acids, the two classes of compounds constituting (+)-1. The structure is secured by NMR spectroscopy and hydrolysis of (+)-1 to give the side-chain moiety ((6R*,2E,4E)-8-hydroxy-6-methylocta-2,4-dienoic acid (2)) intact, whilst the trinor-ermophilane moiety is decomposed. The absolute configuration at the trinor-eremophilane moiety is established from exciton coupling between the dienone and the diene-ester functions.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710107
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  • 158
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    Metal Complexes with Macrocyclic Ligands. Part XXVI.Part XXV: [1] Synthesis and spectral properties of Cu2+ complexes with mono-N-functionalized 1,4,8-trimethyl-1,4,8,11-tetraazacyclotetradecanes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 100-106 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of mono-N-functionalized 1,4,8-trimethyl-1,4,8,11-tetraazacyclotetradecanes 3-14 were synthesized by alkylating the secondary N-atom of the macrocycle 1. The spectral properties of the Cu2+ complexes, studied under different pH conditions, are discussed in relation to the possibility of coordination of the donor group of the side chain to the axial position of the metal ion and to the effect of the length of the side chain.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710112
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  • 159
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    Light-Induced Synthesis of Tricyclic Thiolane Derivatives from 2(5H)-thiophenones via consecutive radical ring closure (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 502-506 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two α,β-unsaturated thiolactones, 5-(2-propynyl)-2(5H)-thiophenone (5) and 3,5-di(2-propenyl)-2(5H)-thiophenone (6), were newly synthesized. Irradiation (λ = 300 nm) of 5 in MeOH containing cyclopentene afforded a 3:1 mixture of diasteroisomeric methyl 7-thiatricyclo[6.4.0.02,6]dodec-10-ene-12-carboxylates (8a/8b), while irradiation of 6 in MeOH saturated with 2-methylpropene gives a 3:2 mixture of diastereoisomeric methyl 3,3,9-trimethyl-5-thiatricyclo[6.2.1.02,6]undecane-1-carboxylates (10a/10b).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710225
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  • 160
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    Dediazoniations of arenediazonium ions part 25Part 24: See Nakazumi et al.[1]. Influence of Substituents on the Exchange of the Diazonio Group for External Molecular Nitrogen and on the N(α), N(β)-Rearrangement in the Diazonio Group (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 507-514 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The N(α), N(β)-rearrangement of the two N-atoms which can be observed in solutions of [β-15N]-labelled p-substituted benzenediazonium ions follows dual substituent parameter treatments. The reaction yields a negative field and a positive resonance reaction constant (pF =-3.35, pR = 2.47). The magnitude of these constants is, within experimental error, the same as the respective reaction constants for solvolytic dediazoniation. The exchange of the diazonio group of 15N-labelled p-substituted benzenediazonium ion yields, however, field and resonance reaction constants which are close to zero. This result is attributed to cancellation of the reaction constants for the forward and reverse steps in the complex mechanism of the exchange reaction.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710302
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  • 161
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    15N-Markiertes 3-(Dimethylamino)-2,2-dimethyl-2H-azirin zur mechanistischen Untersuchung von Reaktionen mit NH-aciden HeterocyclenVorgetragen (H.H.) anlässlich der Herbstversammlung der Schweizerischen Chemischen Gesellschaft, 16. Oktober 1987, Bern.Herrn Prof. Dr. Max Viscontini zum 75. Geburtstag gewidmet (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 521-530 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N-Labelled 3-(Dimethylamino)-2,2-dimethyl-2H-azirine for Mechanistic Studies of Reactions with NH-Acidic HeterocyclesThe synthesis of 3-(dimethylamino)-2,2-dimethyl(1-15N)-2H-azirine (1*) was accomplished via reaction of 1-chloro-N,N,2-trimethyl-1-propenylamine (9) and sodium (1-15N) azide (Scheme 3). The earlier reported reactions of 1 with saccharin (10, Scheme 4), phthalimide (12, Scheme 5), and 2H-1,3-benzoxazin-2,4(3H)-dione (16, Scheme 6) were repeated with 1*, and the position of the 15N-label in the products was determined by 15N-NMR spectroscopy. Whereas the postulated reaction mechanisms for 10 and 12 were confirmed by these experiments, the mechanism for the reaction of 16 had to be revised. With respect to the position of 15N in the products 17 and 18, a new mechanism is formulated in Scheme 7. Treatment of 5,5-dimethyl-1,3-oxazolidine-2,4-dione (19) with 1* led to 3,4-dihydro-2H-imidazol-2-on 20 in which only N(3) was labelled. The mechanism of a ring expansion and transannular ring contraction as shown in Scheme 8 is in agreement with this finding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710304
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  • 162
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    Complexation of Cu2+ by Binucleating Macrocycles Containing the N6 Donor Set (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 562-568 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hexadentate ligands 1,4,7,12,15,18-hexaazacyclododecosane ([2]aneN6) and 1,4,7,14,17,20-hexaazacyclohexacosane ([26]aneN6) both form eight complexes with Cu2+, three of them being binuclear. The corresponding stability constants have been determined potentiometrically, and the electronic absorption spectra have been obtained from spectrophotometric data. Possible interactions of the Cu2+ pairs in the three binuclear complexes have, in addition, been investigated by ESR and and linear -sweep voltammetry (LSV). The binuclear complex of [22]aneN6 with one addditional OH group is exceptionally stable, ESR-silent, and the results of the LSV-experiments are characteristically different from those of the other binuclear complexes with both ligands. This indicates that [22]aneN6 forms a very stable hydroxo-bridged binuclear Cu2+ complex Cu2L(OH)3+, whereas in the case of [26]andN6 no bridged Cu2+ pair exists.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710308
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  • 163
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    Sambucinic Acid, a New Metabolite of Fusarium sambacinum. 45th communication on verrucarins and roridins44th Communication: [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 588-595 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sambucinic acid (5), a C15-trichothecene with a modified strure, has been isolated from cultures of Fusarium sambucinum. The structure is established by spectroscopic data and X-ray diffraction analysis. A hypothetical biogenetic pathway is proposed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710311
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  • 164
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    A Stereoselective Synthesis of (±)-cis-γ-Irone (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 619-623 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-cis-γ-Irone(1), a main constitutent of natural iris oil, has been stereoselectively synthesized from methyl (2E)-3 -[(2,2,4-trimethyl-3-cyclohexen-1-yl)methoxy]-2-propenoate (3) (6 steps, overall yield 14%). The cis-configuration as the exocyclic position of the double bond of 1 were secured by the thermal ene reaction of the β-(alkenyloxy)acrylate 3 yielding the 3-oxabicyclo [3,3,1] nonane derivative 5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710315
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  • 165
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    Amide-Bond Syntheses Catalyzed by Penicillin Acylase (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 631-641 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enzymatic synthesis of amide bonds catalyzed by penicillin acylase is investigated both in H2O solution and in organic solvents containing reverse micelles. The specificity of the reaction is rather high on the side of the acyl component, practically only phenylacetic acid gives sizeable yields. On the contrary, a variety of amino-acid esters, dipeptides, and tripeptides can be used as amino component, e.g., serine methyl ester, methionine ethyl ester, tyrosine ethyl ester, Gly-Asp, Ala-Tyr, Gly-Tyr-Gly etc. However, Many other amino-acid residues do not react, and the possible reasons for this are discussed. Yields varyin rang the 10-80%. A. systematic study to optimize yields by varying the solvent composition is presented for one model reaction. The enzyme is also able to couple certain D-amino-acid residues (e.g. D-methionine ethyl ester or Gly-D-Asp) though at lower rate. Reverse micelles formed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) in CHCl3/isooctane are used to host penicillin acylase and to perform amide synthesis in which the product is perferentially soluble in the organic solvent mixture. The reaction is studied as a function of pH and certain micellar parameters, e. g. wo (wo = [H2O]/[CTAB]). A new membrane enzyme reactor is utilized to separate the product from the enzyme-containing micelles. The adavantges and the limits of this approach are discussed.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710317
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  • 166
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    Photophysical Properties and Photochemical Behaviour of Ruthenium(II) complexes containing the 2,2′-bipyridine and 4,4′-diphenyl-2,2′-bipyridine ligands (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 733-741 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the emission lifetime of the series of complexes Ru(bpy)n(4,4′-dpb)2+3- (bpy = 2,2′bipyridine, 4,4′-dpb = 4,4′-diphenyl-2,2′-bipyridine) has been studied in propionitrile/butyronitrile (4:5 v/v) solutions in the range 90-293 K. The obtained photophysical parameters show that the energy separation between the metal-to-ligand charge tranfer (3MLCT) emitting level and the photoreactive metal-centered (3MC) level changes across the series (ΔE = 3960, 4100, 4300, and 4700 cm-1 for Ru(bpy)2+3), Ru(bpy)2(4,4′-dpb)2+, Ru(bpy)(4,4′-dpb)2+2, and Ru(4,4′-dpb)2+3, respectively, where ΔE is the energy separation between the minimum of the 3MLCT potential curve and 3MLCT - 3MC crossing point. Comparison between spectral and electrochemical data indicated that the changes in ΔE are due to stabilization of the MLCT levels in complexes containing 4,4′-dpb with respect to Ru(bpy)2+3. The photochemical data for the same complexes (as I- salts) have been obtained in CH2Cl2 in the presence of 0.01M Cl- upon irradiation at 462 nm. The complexes containing 4,4′-dpb are more photostable than Ru(bpy)2+3. Comparison between the data for thermal population of the 3MC photoreactive state and those for photochemistry indicated that the overall photochemical process is governed by (i) a thermal redistribution between the emitting and photoreactive excited states, and (ii) mechanistic factors, likely related to the size of the detaching ligand.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710407
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  • 167
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    8-Aza-7-deaza-2′,3′-dideoxyguanosine: Deoxygenation of its 2′deoxy-β-D-ribofuranoside (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 757-761 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 6-amino-1-(2′,3′-dideoxy-β-D-glycero-pentofuranosyl)-1H-pyrazolo[3,4-d]pyrimidin-4(5H)-one ( =8-aza-7-deaza-2′,3′-dideoxyguanosine; 1) from its 2′-deoxyribofuranoside 5a by a five-step deoxygenation route is described. The precursor of 5a, 3a, was prepared by solid-liquid phase-transfer glyscosylation which gave higher yields (57%) than the liquid-liquid method. Ammonoloysis of 3b furnished the diamino nucleoside 3c. Compound 1 was less acid sensitive at the N-glycosydic bond than 2′,3′-dideoxyguanosine (2).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710410
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  • 168
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    Novel Aplysinopsin-Type Alkaloids from Scleractinian Corals of the Family Dendrophylliidae of the Mediterranean and the Philippines. Configurational-assignment criteria, stereospecific synthesis, and photoisomerization (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 773-782 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the scleractinian coral Tubastraea sp. (Dendrophylliidae) collected at Palawan, Philippines, 3′-deimino-3′-oxoaplysinopsin (4) and 6-bromo-3′-deimino-3′-oxoaplysinopsin (6) are now isolated as 5:2 mixtures of (E/Z) stereoisomers. The 3′-deimino-2′,4′-bis(demethyl)-3′-oxoaplysinopsin (7) and 6-bromo-3′-demino-2′,4-bis(demethyl)-3′-oxoaplysinopsin (5) are isolated as 2:3 and 1:1 (E/Z) mixtures, respectively, from another dendrophylliid, Leptopsammia pruvoti, collected near Marseille, Mediterranean coast of France. Larger amounts of these and related compounds, needed for a full structural determination, are obtained by synthesis. Thus, condensations of indol-3-carboxaldehyde (9) or of its 6-bromo derivative 14 with hydantoin (15), 3-methylhydantoin (11), or 1,3dimethylhydantoin (10) give the prevalent natural aplysinopsins with high stereospecificity. The minor stereoisomers (Z)-4, (Z)-6, (E)-7, and (E)-5 are obtained by (E/Z) photoisomerization under UV light of the condensation mixtures. The configuration is assigned from larger H—C(8)/C(5′) 1H, 13C couplings in the (E) than in the (Z) isomer, and, in the case of 4 and 6, from NOE enhancement at Me—N(2′) on irradiation at H—C(8). The stereospecificity of the condensations is attributed to steric inhibition to planarity in the rate-limiting transition states, due to N(2′)/H—C(2) repulsion with (Z)-4 and (Z)-6, or to C(5′)=O/H—C(2) repulsion with (E)-7 or (E)-5. As the aplysinopsins undergo (E/Z ) phostoisomerization also under the daylight conditions of the laboratory, their isomeric composition in nature can not be presently assessed.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710412
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  • 169
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    Synthèses et caractérisation d'une nouvelle classe de sels de flavylium; voie d'accès aux composés du type (acétoxy-2-phényl)2-méthylidène-4-4H-benzopyranne-1. Structure radiocristallographique de l'(acétoxy-2-méthyl-5-phényl)-2-diméthyl-4, 6-benzopyranne-1-ylium pentachlorostannate: mise en évidence de ponts chlore dans l'uniteé decachlorodistannate(2-) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 812-817 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis and Characterization of a New Class of Flavylium Salts; a Facile Route to the 2-(2-Acetoxyphenyl)-4-methylidene-4H-1-benzopyran Derivatives. X-Ray Crystal Structure of 2-(2-Acetoxy-5-methylphenyl)-4,6-dimethyl-1-benzopyranylium Pentachlorostannate: Supporting evidence of Chlorine Bridging in the Decachlorodistannate(2-) UnitSeveral mixtures of compounds 1 and 2 were synthesized from SnCl4 and p-substituted aryl acetates. Separation of 1/2 was achieved either by treatment of the mixture with MeCN providing the pure complex 1 or by reaction with MeCOCl leading selectively to a new class of flavylium salts 3 or 4. The structure of 2-(2-acetoxy-5-methylphenyl)-4,6-dimethyl-l-benzopyranylium pentachlorostannate (3a) was determined by single-crystal X-ray diffraction. The Sn-atoms are hexacoordinated in the dimeric unit Sn2Cl2-10 through Cl bridging. Furthermore, we report the easy preparation of 1-benzopyran derivatives starting from the salts 3.
    Notes: NO ABSTRACT.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710416
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  • 170
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    Stereospecific Synthesis of 2-Oxazinyl-4-oxoazetidinecarbamates Starting from a 1,2-Diazepine. A new type of intramolecular transbenzoylationDedicated to Professor Edward C. Taylor at the occasion of his 65th anniversary. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 822-834 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azeitidinodiazepines 4b and 4c react with acylnitroso dienophiles 5a-c, specifically from their convexe α-side, but in a non-regiospecific way, leading thereby stereospecifically to the expected adducts 6a-d and 7a-d. The three-dimensional structures of 6a and 7a were determined by X-ray analyses which corroborated their NMR data. OsO4 cis-glycolization occurred in good yield with the inverse adducts 7a and 7e and led to the rearranged products 10. These latter ones result from an intramolecular N- to O-transbenzoylation of the short-lived intermediates 9 followed by fragmentation of the animal function. X-Ray analysis of 7a showed the N(10) atom to be pyramidal, a result which demonstrates that it does not have any pronounced benzamide character; otherwise no such N- to O-transbenzoylation would have taken place. Structure and relative configuration of 10a were ascertained by X-ray analysis which confirmed its NMR data as well as the stereochemical outcome of its formation.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710418
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  • 171
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    Thermal and Photochemical Oxetane Formation. A Contribution to the Synthesis of Branched-Chain AldonolactonePart 4 of ‘Thermal Reactions of Donor-Acceptor Systems’; for Part 3, see [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 981-987 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Derivatives of 2-C-branched-chain erythrono-1,4-lactones of the types 1 have been synthesized under reductive conditions using DIBAL from the oxetane 2, which is easily accessible from diethyl mesoxalate (4) and 2,2-diisopropyl-1,3-dioxole (3) in high yield by means of a catalytic cycloaddition. Similarly, 2 rearranges in presences of AlMe3 under formation of an erythronolactone with an additional branching at C(4). The corresponding oxetanes 7-9 from ethyl pyruvate (5) and ethyl trimethylpyruvate (6), respectively, have been studied with regard to their reductions yielding building blocks of branched-chain sugars.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710506
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  • 172
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    Aldehyde Enol Esters as Novel Chain Terminators in Cationic Olefin Cyclizations (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1000-1004 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Citronella (1) has been transformed into enol acetates 2 which have been cyclized with various Lewis and Brönsted acids to dihydrocyclocitral (4). Application of this methodology to the synthesis of mono- and bicyclic ring systems has been examined.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710509
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  • 173
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    Synthesis of Ethyl (2RS,3SR)-1-Tosyl-3-Vinylazetidine-2-carboxylate and ethyl (2RS,E)-3-ethylidene-1-tosylazetidine-2-carboxylate (=rac-ethyl N-tosylpolyximate)This work is part of the Ph. D. thesis of H. B. [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1025-1034 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 3-ethylideneazetidine-2-carboxylic acid (=polyoximic acid; 3) is a approached in two different ways leading to potential precursors of 3. The first way involved a ring closure to a vinyl-subsatituted azetidin. Thus, Ireland-Claisen rearrangement of the Boc-glycinates 6 and 10 of (Z)- and (E)-2-butene-1,4-diol afforded, after exchange of the N-protecting groups, the isomeric 2-(tosylamino)-3-vinylbutanolides 13 and 14 with high stereoselectivity. Only the cis-isomer 14 could be further transformed to 3-(bromomethyl)-2-(tosylamino)-4-pentenoate 17, and in a smoth cyclization with K2CO3, to trans-3-vinylazetidtene-2-carboxylaze 18 (Scheme 2). In the second approach, the 3-ethylidene isomer 19 of 18 was obtained more directly by a [2+2] cycloaddition, together with the two isomers 23 and 24, from methlallene 20 and (tosyliminno)acetate 21 (Scheme 3). The main product of this reaction was, however, 2-(tosylamino)-4-hexinoate 22, the product of an ene reaction.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710513
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  • 174
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    Applications of ENDOR Spectroscopy to Radical Cations in Freon Matrices. Part 1. The radical cation of s-trans-buta-1,3-diene (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1065-1068 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Precise values of the proton coupling constants have been determined from the ENDOR spectra of the radical cation of s-trans-buta-1,3-diene generated from the neutral compound by γ irradiation in a CFCl3 matrix at 77 K. These values are 1.119 and 1.050 mT for the pairs of exo- and endo-protons in the 1,4-positions, respectively, and 0.283 mT for the pair of protons in the 2,3-positions. A general TRIPLE resonance spectrum proves that all coupling constants have the same sign which should be negative by theory, Evidence by experiment and theory indicate that the s-trans-configuration of the neutral compound is retained upon ionization.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710518
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  • 175
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    Synthese neuer schwefel- und selen-haltiger ‘Donor-Akzeptor-stabilisierter’ Molekülsysteme mit zentraler bicyclo[4.4.1]undeca-4,6,8,10-tetraen-2,3-diyliden- oder Bicyclo[4.4.1]undeca-3,6,8,10-tetraen-2,5-diyliden-GruppeIn Verehrung und Dankbarer Erinnerung an David Ginsburg, TECHNION, Haifa/Israel (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1242-1248 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of New Sulfur- and Selenium-Containing ‘Donor-Acceptor-Stabilized’ Systems with Central Bicyclo-[4.4.1]undeca-4,6,8,10-tetraene-2,3-diylidene- or Bicyclo[4.4.1]undeca-3,6,8,10-tetraene-2,5-diylidene GroupsSyntheses of starting materials 3-55 and 8 and of the S- and containing 1,6-methano[10]annulene (=1,6-methanobicyclo[4.4.1]undeca-1,3,5,7,9-pentaene) derivatives 12, 13, 15 and 16 are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710536
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  • 176
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    [1,1-bis (trimethylsilyl)]-1H-cyclopropa [b] napththalene[tricarbonyl-chromium]: The first arene-chromium complex of a cycloproparene (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1328-1330 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [1,1-Bis (trimethylsilyl)]-1H-cyclopropa [b] naphthalene rricarbonylchromium (2) was synthesized by reaction of 1,1-bis (trimethylsilyl) cyclopropa [b] naphthalene (1b) with tricarbonyltris(acetonitrile) chromium.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710543
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  • 177
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    Die röntgenstrukturanalysen von (E)- und (Z)-2-Buten-1,4-diyl-dithiocyanat bei 93 K (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1235-1241 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-Ray Diffraction Analysis of (E)- and (Z)-2-Butene-1,4-diyl DithiocyanateThe crystal structure of the (E)- and (Z)-2-butene-1,4-diyl dithiocyanate (1 and 2, respectively) which have been used as substrates for an E′ reaction, has been determined by X-ray analysis. The SCN groups are for both molecules in an anticlinal conformation relative to the double bond. A remarkable intermoecular contact has been observed between the N-atom of one molecule and the S-atom of its neighbour.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710535
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  • 178
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    Conformational Flexibility of the Acetoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1281-1290 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformation of the acetoxyphenyl fragment shows a planar acctoxy (AcO) group perpendicular to the Ph ring. Steric hindrance strongly limits and affects rotation about the C—OCOCH3 bond: if the AcO group twists away from its perpendicular conformation, the carbonyl oxygen moves to keep the nonbonded distance to the atoms in ortho-position maximal. This is achieved by some twisting about the O—COCH3 bond correlated with angle bending at the ipso-C-atom and ester O-atom. The maximum observed deviation away from the perpendicular conformation is ∼ 47°. In the case of one or two ortho-hydrogens, deviations of the AcO group from the perpendicular conformation tend to be larger than in the case of two substituents.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710539
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  • 179
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    The Reaction of 3-(Dimethylamino)-2H-azirines with 2,3-Pyridinedicarboximide (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1319-1327 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2,2-dialkyl-3-(dimethylamino)-2H-azirines 1a and 1b with 2,3-pyridinedicarboximide (4) in MeCN or DMF at room temperature yielded two regioisomeric tricyclic 1:1 adducts, the azacyclols 11/12 and 16/17, respectively (Schemes 3 and 4). The structure of 12 was established by X-ray crystallography. Methanolysis of 11/12 and 16/17 led to mixtures of methyl [4, 4-dialkyl-5-(dimethylamino)-4H-imidazol-2-yl] pyridine carboxylates 13/14 and 18/19, respectively. The structure of compound 14 is closely related to that of the powerful herbicide 9 (Scheme 9), i.e. the described reactions offer a new synthetic approach to this class of compounds. A mechanistic interpretation for the formation of regioisomeric 1:1 adducts as well as methyl (imidazol-2-yl) pyridine carboxylates is depicted in Scheme 5.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710542
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    A Synthesis of 1D- and 1L-myo-Inositol 1,3,4,5,-Tetraphosphate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1367-1378 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthesis of 1D- and 1L-myo-inositol 1,3,4,5,-tetraphosphate (1a and 1b resp.) is described. The dibenzylated myo-inositola 9a and 9b, which, by phosphorylation, gave 1a and 1b, respectively, were prepared via two routes. On the one hand, the racemate 3a/3b, obtained from myo-inositol, was resolved by its transformation into the diastereoisomeric carbamates 5a and 5b. Benzylation and deprotecton of 5a and 5b gave the enantiomers 9a and 9b, respectively. On the other hand, treatment of the diester 18 with pig liver esterase gave the ester 21a with high enantiomeric excess. Benzylation and deprotection of 21a yielded 9b. The dibenzyl derivative 9a was obtained using the same enzymatic hydrolysis followed by a protection-deprotection sequence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710548
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    Pteridines. Part LXXXVIIPart LXXXVI [1].. Synthesis and Properties of 8-Substituted 2-Thiolumazines (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1379-1391 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various 8-substituted 2,8-dihydro-2-thioxopteridin-4(3H)-ones (14-21) and 2-(methylthio)pteridin-4(8H)-ones (27-32) have been synthesized by condensation of the appropriate 5-amino-6-(substituted amino)-1,2-dihydro-2-thioxopyrimidin-4(3H)-ones (22-34) and 5-amino-6-(substituted amino)-2-(methylthio)pyrimidin-4(3H)-ones (25, 26), respectively, with glyoxal, biacetyl, and benzil. The presence of a quinonoid cross-conjugated π-electron system makes this type of compounds susceptible to nucleophilic additions in position 7, which leads to intramolecular (43, 45) and intermolecular (44) covalent adducts. The newly synthesized compounds have been characterized by elemental analyses, pKa determinations, 1H-NMR and UV spectra. UV-Spectral changes in dependence of the pH are associated with the most appropriate molecular species including the monocations, neutral forms, covalent adducts, mono- and dianions.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710602
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  • 182
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    Synthesis and Steroidogenic Activity of Covalently Dimerized Corticotropin (ACTH) FragmentsAbbreviations for amino acids and derivatives follow the recommendations of the IUPAC-IUB Joint Commission on Biochemical Nomenclature [1]. Further abbreviations: DMF = N, N′-dimethylformamide, DCCI = N, N′ -dicyclohexylcarbodiimide, SDS = sodium dodecyl sulfate, FPLC = fast protein liquid chromatography. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1421-1428 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical synthesis by classical methods in solution of a dimer of the sequence 1 to 24 of adrenocorticotropin(ACTH) is described. The two monomers were covalently linked through their C-termini, using lysine amide as spacer. Dimerization did not improve significantly the potency of the agonist ACTH-(1-24), while it strongly potentiated the antagonistic effect of the fragments ACTH-(11-24) and ACTH-(7-24) in the stimulation of steroidogenesis in isolated adrenal cells. The results seem to imply a microaggregation of the receptors at the adrenal cell surface.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710606
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  • 183
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    Intramolecular Dynamics of Five-coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable-pressure 1H-NMR spectroscopy (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1458-1466 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variable-pressure 1H-NMR Spectroscopy has been used to study the fluxionality of some five-coordinated Fe complexes in solution. For [Fe(CO)2 1,3-cyclooctadiene (PPh3)], the CO site exchange is known (by analogy with [Fe(CO)3(1,3-cyclooctadiene)]) to be a non-dissociative process, and an activation volume of ca. 0 cm3.mol-1 was indeed obtained. However, for [Fe(CO2){2,3-η:O-σ-(7,7-dimethoxybicyclo[2.2.1]hept-2-ene)}(PPh3)], the activation volume of +5 cm3 mol-1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO)2(1,3-cyclooctadiene)(PPh3)] was ascertained by single-crystal X-ray diffractometry. The crystals are triclinic, space group P1, a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic C=C bond and PPh3 occupying basal sites.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710609
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  • 184
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    The mild bromination of adamantane and (trimethylsilyl) adamantanes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1508-1510 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small amounts of H2O or MeOH catalyze the reaction of Br2 with adamantane and its 1-(trimethylsilyl) and 1,3-bis(trimethylsilyl) derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710616
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  • 185
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    Solid-Phase Synthesis of Oligodeoxynucleotides containing phosphoramidate internucleotide linkages and their specific chemical cleavage (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1517-1527 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligonuclecotides bearing phosphoramidate internucleotide linkages can be prepared chemically by standard solid-phase DNA synthesis. Thus, phosphoramidate internucleotide bonds can be placed at will into specific positions within a given DNA fragment. The backbone-modified DNA fragments prepared in this way are susceptible to a specific chemical cleavage.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710618
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  • 186
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    Semicorrin metal complexes as enantioselective catalysts. Part 2. Enantioselective cyclopropane formation from olefins with diazo compounds catalyzed by chiral (semicorrinato)copper complexesTaken in part from the Ph.D. thesis of H.F., ETH-Zürich (in preparation); for a preliminary communication, see [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1553-1565 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copper complexes of chiral, C2-symmetric semicorrin ligands were found to be efficient catalysts for the cyclopropane formation from olefins with diazo compounds. In the presence of 1 mode-% of catalyst, alkyl diazoacetates reacted smoothly with terminal olefins such as styrene, butadiene, and 1-heptene to give the corresponding optically active cyclopropanecarboxylic-acid derivatives (Table 1 Scheme 2). With one of the catalysts, enantioselectivities up to 97% ee were obtained (Table 2). Usually, the reactions were carried out using bis(semicorrinato)copper(II) complexes as precatalysts. In order to produce active catalysts, these complexes had to be activated first by heating in the presence of diazoacetate or by treatment with phenylhydrazine. Experiments with (semicorrinato)copper(I) complexes, prepared in situ from copper(I) tert-butoxide (Scheme 4), suggest that the actual catalyst is a [mono(semicorrinato)]copper(I).
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710621
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  • 187
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    Photoinduced Double Addition of Acetylene to 3-Oxocyclopent-1-ene-1-carbonitrile or 3-oxocyclopent-1-enyl acetate leading to 2,3-dihydro-1H-inden-1-one and other rearranged products (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1608-1615 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: UV Irradiation of 3-oxocyclopent-1-enyl acetate (17) and acetylene in MeCN at 0° gives, besides the product of normal enone-alkyne [2 + 2] cycloaddition (cis-4-oxobicyclo[3.2.0] hept-6-en-1-yl acetate, 18) and its product of oxa-di-π-methane rearrangement (5-oxotricyclo[4.1.0.02,7]hept-2-yl acetate, 19), unexpected products of further addition of a molar equivalent of acetylene. These are indanone ( = 2,3-dihydro-1H-inden-1-one, 16), in 21% yield, cis-1-cisoid-1,2-cis-2- (20) and cis-1-transoid-1,2-cis-2-7-oxotricyclo[4.3.0.02,5]non-3-en-1-yl acetate (21), 4-oxo-7-‘exo’-vinyltricyclo[3.2.0.02,6]hept-2-yl acetate (22), cis-4-oxo-6-‘endo’- (23) and cis-4-oxo-6-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate (24), and cis-4-oxo-7-‘exo’-vinylbicyclo[3.2.0]hept-1-yl acetate (25). At least in part, indanone must be formed via intermediates 20 and 21. In fact, on heating a 9:1 mixture 20/21, indanone is obtained quantitatively. With 3-oxocyclopent-1-ene-1-carbonitrile (15) in place of 17, indanone is formed in lower (8%) yield besides much tars.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710704
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  • 188
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    Struktur und Partialsynthese von dimerem Coleon F (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1638-1641 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structure and Partial Synthesis of Dimeric Coleon FColeon F (1a), on standing in solution, slowly dimerizes to the labile C(7)-epimeric spiro-dihydrofuranes 2a/2b whose structures were elucidated by spectroscopic methods. Oxydative addition of 1a to another molecule of 1a in the presence of Fétizon's reagent rapidly yields 2a/2b, thus confirming their structures as (4bS,9RS,10′aS)4,4a,10′,10′a-tetrahydro-1′,6-dihydroxy-1,2,4a,7′,8′,10′a-hexamethyl-3′,7-bis(2-propenyl)-spiro[3H,9H-phenanthren-9,5′-5′H-phenanthro[1,10-bc]furan]-2,3,5,8,9′-pentone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710708
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  • 189
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    The Radical Anions of N,N′-Dicyanoquinone Diimines, a New Class of Electron Acceptors (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1665-1672 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anions of 12 N,N′-dicyanoquinone diimines, a new class of electron acceptors, hace been characterized by their hyperfine data with the use of ESR and ENDOR spectroscopy. The largest coupling constant (0.30-0.45 mT), due to the two 14N nuclei in the exocyclic positions, gives rise to a conspicuous broadening of the peripheral ESR lines by an incomplete averaging of the hyperfine anisotropy. The most plausible interpretation of the experimental results for the radical anions of N,N′-dicyano- 1,4-benzoquinone diimine (1) and N,N′-Dicyano-9,10-anthraquinone diimine (9) is in terms of both ‘syn’- and ‘anti’-configurations contributing to the ESR and ENDOR spectra and having equal proton- and 14N-coupling constants. The π-spin distribution in the radical anions of N,N′-dicyanoquinone diimines is compared with those in the analogous ions of tetracyanoquinodimethanes and quinones.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710712
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  • 190
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    Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′-dimethylbiphenyl-2,2′-diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues, and their use in Rh(I)-catalyzed asymmetric isomerizations of N,N-diethylnerylamine (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 897-929 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The axially dissymmetric diphosphines (-)-(R)- and (+)-(S)-(6-6′-dimethylbiphenyl-2,2′-diyl)bis(diphenyl-phosphine) ((-)-(R)-10 and (+)-(S)-10; ‘BIPHEMP’) have been synthesized, starting from (R)- and (S)-6,6′-dimethylbiphenyl-2,2′-diamine ((R)- and(S)-16), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′- dimethyl- and 4,4′-bis(dimethylamino)-substituted analogues 11 and 12 respectively, and the 6,6′-bridged analogues 1,11-bis(diphenylphosphino)-5,7-dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)- and(S)-enantiomers via complexation with di-μ-chlorob is {(R)-2-[1-(dimethylamino)ethyl]pheny-C—N}dipalladium(II) ((R)-18). The molecular structures of the diphosphines (S)-10 and (R)-13 and of two derived cationic Rh(I) complexes,[Rh((S)- 10)(nbd)]BF4 and [Rh((R)- 13)(nbd)]BF4 were determined by x-ray analyses. Absolute configurations were established for (+)-(S)- 10 by X-ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (-)-(R)- 13 by X-ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of 1H-NMR comparisons. The BIPHEMP ligand 10 and analogues 11, 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry-inducing ligands in Rh(I)-catalyzed isomerizations of N,N-diethylnerylamine affording citronellat enamine of 98-99% ee.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710427
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  • 191
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    Synthese von enantiomerenreinen Violaxanthinen und verwandten Verbindungen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 931-956 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of Enantiomerically Pure Violaxanthins and Related CompoundsThe epoxides 16 and ent-16, prepared by Sharpless-Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)-(S)-didehydrovomifoliol (45), (+)-(6S, 7E, 9E)-abscisic ester 46, (+)-(6S, 7E, 9Z)-abscsic ester 47, (-)-(3S, 7E, 9E)-xanthoxin (49), (-)-(3R, 7E, 9E)-xanthoxin (50), (3S, 5R, 6S, 3′S,5′R, 6′S, all-E)-violaxanthin (1) (3R, 5R,6S,3′R,5′R,6′S, all-E)-violaxanthin (55) and their (9Z) (see 53, 57), (13Z) (see 54, 58), and (15Z) (see 60) isomers. The novel violadione (61) was prepared from 1 by oxidation with DMSO/Ac2O. By base treatment, 61 was converted into violadienedione (62), a potential precursor of carotenoids with phenolic end groups.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710502
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  • 192
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    Isolation from the Mediterranean Stolonifern Coral Sarcodictyon roseum of Sarcodictyin C, D, E, and F, novel diterpenodic alcohols esterified by (E)- or (Z)-N(1)-methylurocanic acid. Failure of the carbon-skeleton type as a classification criterionPresented by F. P. as a part of a lecture at the University of Hawaii at Manoa, Honolulu, December 9th, 1987. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 964-976 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown here that the stoloniferan coral Sarcodictyon roseum of east Pyrenean waters contains four novel diterpenoids, sarcodictyin C ((-)-3), D ((-)-4), E ((+)-5), F ((+)-6), which are related to sarcodictyin A ( = (-)-(4R,4aR,7R,10S,11S,12aR,1Z,5E,8Z-7,10-epoxy-3,4,4a,7,10,11,12,12a-octahydro-7-hydroxy-6-(methyoxycarbonyl)-1,10-dimethyl-4-(1-methylethyl)-benzocyclodecen-11-yl (E)-N1-methylyrocanate; ((-)-1), previously isolated from the same coral. Sarcodictyin C ((-)-3) and D ((-)-4) and the 3α-hydroxy and 3α-acetoxy derivatives of (-)-1), sarcodictyin E ((+)-5) is the (Z)-urocanate isomer of (-)-3), and sarcodictyin F ((+)-6) is the 1α-hydroxy-2-ene isomer of (-)-3. In all cases, the nine-membered ring is locked, and the molecule stabilized, by the urocanic appendage; when this is removed in MeOH/KOH, the C(11)-O- function is free to attack at C(5), and retro-condensations then lead to the ring-contracted butenolides 11 (from (-)-3) or 10 (from(-)-1) with extrusion of the hydroxyfuran nucleus (Scheme 3). Under the same conditions, with (-)-3, the C(3)-O- group competitively attacks at C(5), the hydroxyfuran nucleus is expelled, and aldehyde 14 is formed. Peculiarly, in the reaction of (-)-3 with MeOD/KOD, the ring-contracted butenolide 17 contains D at the 4′-ax position. The sarcodictyins are unique in these chemical properties, not shared by the cladiellanes which have the same C-skeleton.
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  • 193
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    Isolation and Absolute Configuration of β,β-Carotene Diepoxide (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 31-32 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5,6:5′,6′-diepoxy-5,6:5′,6;-tetrahydro-β,β-carotene, isolated from tubers of a white-fleshed variety of sweet potato (Ipomoea batatas LAM.) has been assigned the (5R,6S,5′R,6′S)-chirality on the basis of its HPLC, UV/VIS, and CD data.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710104
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  • 194
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    Halochrome Molekeln. 7. Mitteilung. Synthese und acidobasisches Verhalten substituierter Heteroarenochinazoline (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 33-46 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Halochromic Molecules. Synthesis and Acidobasic Properties of Substituted HeteroarenoquinazolinesWe have synthetized a series of substituted heteroarenoquinazolines. The 90-MHz FT 1H-NMR spectra of starting and final products supported the postulated structures. Fragmentation in the mass spectra also were consistant with the assumed structures. With acid, the compounds partly from ring-opened, intensely coloured triphenylcarbenium salts of the Rhoduline-R type (C. I. 42565). UV/VIS spectra of the salts are discussed on the basis of VEPPP-CI calculations. The ∊pH* curves in buffered MeOH/H2O solutions and the pK* values are determined. The title compounds undergo very complex protonation equilibria.
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  • 195
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    Agnatasterone A and B, Unusual Pregnane Steroids Isolated from the North-East Atlantic Sponge Axinella agnata (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 62-71 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two novel pregnatrienolones isolated in very small amounts from the North-East-Atlantic demosponge Axinella agnata (Tetractinomorpha, Axinellida) are unique in having C(2)=C(3) (or C(3)=C(4)), C(7)=C(8), and C(16)=C(17) bonds and a 12β-OH group which, being strongly H-bonded to a 20-keto group, resists acylation. 1H- and 13C-NMR spectroscopy of the steroids and of products of their selective epoxidation or reduction allow us to propose the structures (+)-12β-hydroxy-5α-pregna-2,7,16-trien-20-one ( = agnatasterone A, (+)-1), and (+)-12β-hydroxy-5α-pregna-3,7,16-trien-20-one ( = agnatasterone B. (+)-5), for the two steroids with minimal recourse to model compounds.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710108
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  • 196
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    Free-Energy Dependence of the Ion Yield of Photo-Induced Electron-Transfer Reactions in Solution (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 93-99 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of photo-induced electron-transfer reactions in MeCN with 9,10-dicyanoanthracene as acceptor and 21 electron donors with transient photoconductivity measurements is reported. The free-ion yield and the rate constant of back electron transfer are determined. For exergonic reactions, the ‘Marcus-inverted’ region is observed. The fit with the theory is best, when a nearly solvent-independent Coulomb term is used in the calculation of the energy balance.
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    URL: http://dx.doi.org/10.1002/hlca.19880710111
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  • 197
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    The Adamantane Rearrangement of Tricyclo[4.2.2.01,5]decane to Tricyclo[5.3.0.04,8]decane (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 124-129 
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    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regioselective generation of the C(2)-carbocation a of tricyclo[4.2.2.01,5]decane (1) by treatment of both corresponding epimeric alcohols 5 and 6 with BF3 and trapping the rearranged tricyclo[5.3.0.04,8]decan-7-yl carbocation b with Et3SiH as hydride-ion donor (ionic hydrogenation) gives the corresponding hydrocarbon 3 as sole product in almost quantitative yield. The latter is a known intermediate in the Lewis-acid-catalyzed rearrangement of 1 to adamantane (4).
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    URL: http://dx.doi.org/10.1002/hlca.19880710115
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  • 198
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    Spectroscopic and Electrochemical Behavior of Cyclometalated Pd(II) Complexes (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 134-139 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absorption and emission spectra, emission lifetimes, luminescence quantum yields, and electrochemical behavior of the complexes Pd(Phpy)2, Pd(Thpy)2, and Pd(bhq)2 (Phpy-, Thpy-, and bhq-, and bhq- are the deprotonated forms of 2-phenylpyridine, 2-(2-thienyl)pyridine, and benzo[h] quinoline, respectively) have been studied, and the results obtained have been compared with those available for Pt(II) and Pt(IV) complexes containing the same ligands. The intense ligand-centered absorption bands below 340 nm are strongly perturbed by matalation, and the absorption features in the 340-450-nm region are likely to include contributions from formally metal-to-ligand charge-transfer transitions. The structured luminescence spectra observed at 77 K (lifetimes are 0.48, 0.28 and 2.6 ms for Pd(Phpy)2, Pd(Thpy)2, and Pd(bhq)2, respectively) have been assigned to transitions having mainly ligand-centered character, with an increasing metal-to-ligand charge-transfer contribution in going from Pd(bhq)2 to Pd(Phpy)2 and to Pd(Thpy)2. The complexes Pd(phpy)2 and Pd(thpy)2 show two reversible one-electron reduction waves, whereas reduction of Pd(bhq)2 is irreversible, as is the oxidation of the three complexes.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710117
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  • 199
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    High-Yield Synthesis of 20-, 24-, and 28-Membered Macropentolide, -hexolide, and -heptolide, Respectively, from (R)- or (S)-3-hydroxybutanoic acid under Yamaguchi's macrolactonization conditionsFor a partial preliminary communication, see our recent review on the use of the biopolymer PHB/PHV for EPC syntheses [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 155-167 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The macrocyclic pentolide 1, hexolide 2, and heptolide 3 constitute ca. 80% of the oligomers formed in ca. 50% yield from enantiomerically pure 3-hydroxybutanoic acid under Yamaguchi's macrolactonization conditions. The FAB mass spectra of the MH+, M Na+, and MCs+ are reported (Figs. 2, 3, 5, and 6). No cyclic tetramer is detected. The 1H-NMR spectra of the cyclic oligomers, of the monomer, and of the polymer (PHB) are very similar (Fig. 4). Directed synthesis of the open-chain dimer and tetramer of 3-hydroxybutanoic acid and attempted cyclization do not lead to the isolation of the cyclic tetramer.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710119
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  • 200
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    Electronic Resource
    Silicon-Directed Nazarov Cyclizations. Part VI. The anomalous cyclization of vinyl dienyl ketones (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 195-208 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions, of various vinyl dienyl ketones (see la-e, li) with FeCl, give rise to β,γ-unsaturated α-vinyl-cyclo-pentenones (see 2a-e, 2i, Table 2). The reaction succeeds for vinyl dienyl ketones with substituents on either double bond. Aryl dienyl and alkyl dienyl ketones (see 1f-h) do not cyclize cleanly. The effects of substituents on the rate of reaction is discussed in terms of the mechanism of the rearrangement. A 13C-labeling study establishes the pathway as an unusual 1-hydroxypentadienyl-cation electrocyclization to a cyclopentenyl cation which collapses via a pinacol rearrangement to the α-vinyl ketone.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710121
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