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  • 1
    Electronic Resource
    Electronic Resource
    Synthese und Eigenschaften von 1,2,4,3-Thiadiazaboretidinen. Kristallstruktur des 2,4-Di-tert-butyl-3-phenyl-1,2,4,3-thiadiazaboretidins (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 47-50 
    Details
    ISSN: 0009-2940
    Keywords: Sulfur diimides ; 1,3-Cycloaddition, reductive ; 1,2,4,3-Thiadiazaboretidines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Properties of 1,2,4,3-Thiadiazaboretidines. Crystal Structure of 2,4-Di-tert-butyl-3-phenyl-1,2,4,3-thiadiazaboretidineReaction of sulfur diimides with alkyl(aryl)bis(methylthio)boranes leads to reductive 1,3-cycloaddition of the NSN sequence with formation of the 1,2,4,3-thiadiazaboretidines 2a-g. NMR (1H, 11B, 13C, 15N, 29Si), mass spectra and the results of the X-ray analysis of 21 are reported and discussed. The 11B chemical shifts have been calculated for 3-phenyl-1,2,4,3-thiadiazaboretidine and some related model compounds by the IGLO method and correlate acceptably with the experimental values.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240108
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  • 2
    Electronic Resource
    Electronic Resource
    Dissoziative Ringöffnung halogensubstituierter Methylcyclopropan-Radikalkationen in der Gasphase (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 1084-1094 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Dissociative Ring Opening of Halogen Substituted Methylcyclopropane Cation Radicals in the Gas PhaseThe unimolecular gas phase reactions of several C4H7Br+· isomers are investigated. Rearrangement of the incipient C4H7+ ion is observed prior to Br· loss from all C4H7Br+· isomers except ionised 2- (9) and 3-methylallyl- (10) and cyclobutylbromides (6). This is evidenced by the increased average kinetic energy release associated with Br· elimination. In addition, the structure of the C4H7+ ions may be established using collisional activation spectroscopy. Ionised 1- and 2-methylcyclopropylbromides both yield 1-methylallyl cation rather than 2-methylallyl cation. MNDO calculations on the analogous C4H7Cl+· isomers lead to similar conclusions; moreover, these calculations shed light on the probable mechanism for both isomerization and decomposition of the molecular ions.
    Notes: Die unimolekularen Zerfälle einiger isomerer C4H7Br+·-Verbindungen werden in der Gasphase studiert. Die Br·-Abspaltung aus ionisiertem Cyclobutylbromid (6) und 2- bzw. 3-Methylallylbromid (9 bzw. 10) erfolgt ohne Isomerisierung des entstehenden C4H7+-Ions. Bei allen übrigen Verbindungen ist die dissoziative Ionisation mit einer Isomerisierung des Kations verbunden. Diese Umlagerung, die vor der eigentlichen Br·-Eliminierung eintritt, manifestiert sich in einer Linienverbreiterung der Übergangssignale („kinetic energy release“). Die resultierenden C4H7+-Kationen lassen sich anhand ihrer Stoßaktivierungsspektren charakterisieren. Aus den Radikalkationen der 1- und 2-Methylbromcyclopropane entsteht bei der Br·-Abspaltung das 1-Methylallylkation und nicht das 2-Methylallylkation. MNDO-Rechnungen für die analogen C4H7Cl+·-Radikalkationen unterstützen die bei den Bromiden gemachten experimentellen Befunde; außerdem enthüllen diese Rechnungen mechanistische Details der unimolekularen Reaktionen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130327
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  • 3
    Electronic Resource
    Electronic Resource
    Gasphasenreaktion von Tetraboran(10) mit Allen: das fluktuierende arachno-1-Carbapentaboran(10)-Isomerensystem und die Derivate 1,2- und 1,3-Me2-1-CB4H8; Analogien bei 1-CB4H10, MeB5H10 und B5H10Diese Arbeit wurde vom Engineering and Physical Sciences Research Council. von der Royal Society, von der Deutschen Forschungsgemeinschaft und vom Fonds der Chemischen Industrie gefördert. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 1542-1544 
    Details
    ISSN: 0044-8249
    Keywords: Ab-initio-Rechnungen ; Bor ; Carborane ; NMR-Spektroskopie ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971091323
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  • 4
    Electronic Resource
    Electronic Resource
    Preparation of Butatrienylamines from Butenynylamines (1982)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 21 (1982), S. 862-863 
    Details
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198208621
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  • 5
    Electronic Resource
    Electronic Resource
    Entartete CarboniumionenAls Abkürzungen werden verwendet: Ac=Acetyl; Bs=Brosyl (p-Brombenzolsulfonyl); t-Bu=tert.-Butyl; DNV=3,5-Dinitrobenzoyl; Et=Äthyl; Me=Methyl; Ph=Phenyl; PNB=p-Nitrobenzoyl; SOH=Lösungsmittel; Ts=Tosyl (p-Toluolsulfonyl). (1970)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 82 (1970), S. 889-919 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Als entartet werden Carboniumionen bezeichnet, wenn sie über endliche Energieschwellen hinweg in Produkte übergehen, deren Gesamtstrukturen mit denen der Ausgangsionen identisch sind. Bei solchen entarteten Umlagerungen („Automerisierungen“) werden die individuellen Atome und Gruppen vermischt, aber die Gesamtstruktur bleibt erhalten. Automerisierungen können beobachtet werden, indem man die Ausbreitung von Isotopenmarkierungen oder den Verlust der optischen Aktivität oder die Temperaturabhängigkeit der NMR-Spektren feststellt. In einigen Fällen führt eine Kombination bekannter Umlagerungsprozesse zum vollständigen Vermischen aller Kohlenstoff- und aller Wasserstoffatome. Das 2-Norbornyl- und das 9-Barbarayl-Kation sind Beispiele für vollständig entartete Systeme; es lassen sich Bedingungen finden, unter denen beide nur Ein-Linien-NMR-Spektren ergeben.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19700822202
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  • 6
    Electronic Resource
    Electronic Resource
    Empirical force-field and ab initio calculations on delocalized open chain cations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 28-44 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Force-field calculations are reported for large delocalized cations. The results for the geometries, heats of formation, and π-electron densities agree well with MP2(full)/6-31G* ab initio calculations. Both methods give similar results for the distortion of the carbon skeletons of unsubstituted cations by hyperconjugating methyl groups. Because of the SCF treatment of π-interactions, the MMP2 force-field technique enables calculations of resonance energies in delocalized cations. The additional resonance stabilization produced by extending conjugation is directly related to the π-charge on the carbon at which a vinyl group is substituted. The good agreement of MMP2 results for nonbonded resonance effects in large delocalized cationic π-systems with ab initio data suggests that MMP2 can be used to study the influence of these interactions in cationic π-systems too large to be calculated by correlated ab initio methods. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    NMR chemical shielding surface of N-Acetyl-N′-Methylalaninamide: A density functional study (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 126-138 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The five energetically lowest minima on the potential energy surface of N-acetyl-N′-methylalaninamide were optimized at the Becke3LYP/DZd level of theory to compare these density functional theory results with the literature findings at restricted Hartree-Fock/3-21G. While the relative energies are very similar, the amide moiety is predicted to be much more flexible at Becke3LYP/DZd. As a consequence, the three minima that favor a nonplanar amide group differ by up to 14° in their φ and ψ values between the two levels. To compare the change in the density functional NMR chemical shifts with respect to φ and ψ with experimental results, Becke3LYP/DZd was employed to optimize a structure for N-acetyl-N′-methylalaninamide at each 30° interval on the (φ, ψ) surface in the regions that correspond to the α helix and the β-pleated sheet and at each 60° interval elsewhere. The corresponding NMR chemical shielding surface was computed with the density functional program deMon. The resultant NMR chemical shielding surfaces for N and Cβ are in good agreement with the experiment, while the change in the NMR chemical shielding of C′ and Cα cannot be described only in terms of φ and ψ. The chemical shifts for those atoms also depend on the nonplanarity of the amide moiety. We evaluated this dependence for N-methylacetamide as a model system. Estimates of the parameters derived from N-methyl-acetamide allowed the NMR-shielding surfaces of C′ and Cα to be corrected for the nonplanar nitrogen influence. Although the effect is less pronounced with lower level theoretical geometries, due to the smaller degree of pyramidalization of the amide nitrogen, the (φ, ψ) NMR chemical shielding surfaces will need to be corrected. The agreement with the experiment was much better for the corrected surface of C′ when the nitrogen in the α helix had a nonplanar environment. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Internal conrotation and disrotation in H2BCH2BH2 and diborylmethane 1,3 H exchangeThis work is dedicated to Professor Ronald Hoffmann on the occasion of his 60th birthday. (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1792-1803 
    Details
    ISSN: 0192-8651
    Keywords: diborylmethane ; conrotation and disrotation ; 1,3 H exchange ; orbital deletion procedure ; gradient line reaction path ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The paths of correlated internal disrotation (barrier less than 0.4 kcal/mol) and conrotation (barrier around 1.9 kcal/mol) of the two BH2 groups in H2BCH2BH2 have been computed employing ab initio [MP2(full)/6-31G**] and density functional theory (Becke3LYP/6-311+G**) methods. Two B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative interactions stabilize the Cs symmetric H2BCH2BH2 isomer (1). The B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative stabilization, evaluated by homodesmotic reactions and using the orbital deletion procedure (which “deactivates” the “vacant” born p orbital), is less than 6 kcal/mol in diborylmethane. The B(SINGLE BOND)C(DOTTED BOND)B(p) stabilization is shown to be remarkably large in C4B6H10 (Td). At MP2(fu)/6-31G**, disproportionation into 1 and methane is only 5.6 kcal/mol exothermic. The 1,3 H exchange in diborylmethane is an asynchronous process and proceeds via a doubly bridged cyclic intermediate with 9.3 kcal/mol barrier. Structures with “planar tetracoordinate” carbon are stabilized considerably by BH2 substituents, but they are still high in energy.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1792-1803, 1997
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    A critical analysis of electronic density functionals for structural, energetic, dynamic, and magnetic properties of hydrogen fluoride clusters (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1695-1719 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We present extensive computational results on density functional calculations for hydrogen fluoride species (HF)n (with 1≤n≤6) and compare them to results from other approaches and experiments, where available. Among the calculated properties we discuss equilibrium structural parameters, vibrational frequencies, electric dipole moments, IR intensities, dissociation energies, barriers for rearrangement by proton tunneling, NMR chemical shifts and spin couplings for 1H and 19F, and magnetic susceptibilities. It is found that density functional (particularly BLYP) and even more so hybrid approaches (particularly B3LYP) provide useful results. However, we show that due to some characteristic deficiencies, these are in general not competitive with more quantitative results from large basis set MP2 calculations. The calculated magnetic properties do not indicate any “aromaticity” connected to a hypothetical electronic ring current.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1695-1719, 1997
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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