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  • 1
    Electronic Resource
    Electronic Resource
    An Analysis of the Bonding Properties of Benz[a]azulene by X-Ray, NMR, and Computational StudiesDedicated to Edgar Heilbronner on the occasion of his 75th birthday (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 837-854 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal structures of 9-phenylbenz[a]azulene (4) and the corresponding non-benzannelated form, 4-phenylazulene (5), have been determined (cf. Fig.2). In contrast to 5, the skeleton of which shows nearly equal C,C bond lengths (cf. Table 1), the seven-membered ring of 4 exhibits clearly alternating C,C bond lengths (cf. Table 1). This is in agreement with a strong accentuation of the heptafulvene substructure in 4 by the [a] benzannelation. The alternating bond lengths of 4 and of its parent structure 3 are also reflected in the corresponding variations of the 3J(H,H) and 1J(13C,13C) values of these benz[a]azulenes (cf. Tables 4 and 5). Computations on the MP2/6-31G* level as well as on the BP86/6-31G* level for azulene (6), benz[a]azulene (3), and heptafulvene (7) are in good agreement with the experimental values (cf. Tables 6-8).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790326
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  • 2
    Electronic Resource
    Electronic Resource
    Computations of 57Fe-NMR Chemical Shifts with the SOS-DFPT Method (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 742-754 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 57Fe Shielding tensors of substituted iron-carbonyl complexes have been computed employing the density-functional-based SOS-DFPT method (sum-over-states density-functional perturbation theory) with the IGLO (individual gauge for localized orbitals) choice of gauge origins and with large basis sets. The shieldings computed for [Fe(CO)5], [Fe(CO)3(H2C=CHCH=CH2)], [Fe(CO)3(cyclo-C4H4)], [Fe(CO)4(H2C=CHOMe)], [Fe(CO)4(H2C=CHCN)], [Fe(CO)3(H2C=CHCH=O)], and [Fe(CO)2(C5H5)R] (R = Me, Bu, i-Pr) correlate with the experimental δ(57Fe) values. However, the slope of the correlation line is 0.55 instead of 1, i.e., only about one half of the substituent effects on σ(Fe) is recovered in the calculations. Nearest-neighbor effects appear to be described qualitatively (cf. in the [Fe(CO)2(C5H5)R] series, whereas effects of more remote substituents, e.g., for [Fe(CO)4(H2C=CHX)] (X = MeO and CN)) are not reproduced. Dissociation energies of these species are discussed because of their relevance to experimental rate constants for substitution processes which are known to correlate with δ(57Fe). Even though the δ(13C) and δ(1H) data of ferrocene (7) are well reproduced theoretically, the computed σ(Fe) shielding of 7 deviates substantially from the σ(calc.)/δ(expt.) correlation, possibly indicating additional shortcomings in the theoretical description of this molecule.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790317
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical investigations of NMR chemical shifts and reactivities of oxovanadium(v) compounds (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 113-122 
    Details
    ISSN: 0192-8651
    Keywords: density-functional theory ; 51V ; chemical shift calculations ; mechanism of ethylene polymerization ; barriers for ethylene insertion ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Employing gradient-corrected levels of density-functional theory (DFT), medium-sized basis sets, and optimized geometries, chemical shifts are calculated for [VOClnF3-n] (n=0-3), VF5, [VO(OCH2CH2)3N], [V(CO)6]-, [V(CO)5(N2)]-, as well as for the model compounds [VO(OMe)nMe3-n] (n=0-3) and their AlH3 adducts. Experimental trends in δ(51V) are well reproduced with DFT-based methods; for example, the slopes of the δ(51V)calc vs. δ(51V)expt linear regression lines are 0.92 and 1.03 at the GIAO-BP86 and GIAO-B3LYP levels, respectively. Ethylene polymerization observed with [V(O⋅⋅⋅AlX3)(OR)nR′3-n] (X, R, R′=bulky alkyl, aryl, or silyl groups) is shown for model systems (X=H, R=R′=Me) to proceed by insertion of the olefin into a V - C bond via a transition state with approximate square-pyramidal coordination about vanadium. For the tri- and dialkyl derivatives (n=0, 1), similar activation barriers of ca. 19 kcal/mol are computed (BP86 level including zero-point energies), whereas that of the monoalkyl species (n=2) is predicted to be much higher, ca. 30 kcal/mol. The relevance of these results for the apparent relationship between δ(51V) and catalytic activities is discussed.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 113-122, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Steric and Electronic Effects on the 103Rh NMR Chemical Shifts of RhI(cyclooctadiene) Compounds Bearing N-Donor Ligands (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 27-33 
    Details
    ISSN: 1434-1948
    Keywords: 103Rh NMR ; Rhodium complexes ; Nitrogen ligands ; Chemical-shift computation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study electronic and steric effects on δ(103Rh), the103Rh-NMR spectra of a series of [Rh(cod)L2] complexes (with L = nitrogen, oxygen, or chloride) have been measured by gradient-enhanced HMQC (1H,103Rh) NMR spectroscopy. Density functional computations of representative examples have been performed at the GIAO-B3LYP level of theory. The obtained experimental values of 103Rh shifts fit the generally observed trend of coordinating ligands in the first coordination sphere of the metal: P 〈 N 〈 O. Calculated 103Rh shifts agreed to within 8 % with experimental values. The computational results indicate that the Rh-N bond distance has a larger influence on the chemical shift than the N-Rh-N angle.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Über die Bindungsverhältnisse in Pyrazolylboran, eine ab-initio/IGLO/NMR-StudieProfessor Günther Wilke zum 65. Geburtstag gewidmetDiese Arbeit wurde von der Deutschen Forschungsgemeinschaft, dem Fonds der Chemischen Industrie, der Convex Computer Incorporated und der Volkswagen-Stiftung gefördert. Wir danken der Kernforschungsanstalt Jülich für Rechenzeit und sind Prof. W. Kutzelnigg und seinen Mitarbeitern für die Entwicklung des IGLO-Programms, M. Schindler für die Convex-Version und U. Fleischer für Diskussionen, ausführliche MNDO-Rechnungen und weitere experimentelle Informationen. (1990)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 102 (1990), S. 320-322 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19901020325
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  • 6
    Electronic Resource
    Electronic Resource
    The structures of the hypho-compounds B5H12- and B6H14: Application of the combined ab initio/IGLO/NMR methodPresented in part at the Seventh International Meeting on Boron Chemistry (IMEBORON VII) from July 29 to August 3, 1990, in Torun, Poland. (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Heteroatom Chemistry 2 (1991), S. 499-506 
    Details
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio and NMR chemical shift (IGLO) calculations on the TZP/MP2/6-31G* level suggest a Cs (1c), or the closely related C1 (1d) structure, rather than the proposed C2v (1a) geometry for hypho-B5H12-. The two equivalent Cs forms interconvert rapidly with a barrier of ca 5 kcal/mol. For hypho-B6H14 (2), at least six isomers examined lie within ca 7 kcal/mol in energy suggesting fluxional behavior, but none of the geometries (including the current proposals in the literature) reproduces the experimental chemical shifts.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hc.520020413
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Decaethyl-2,6,8,10-tetracarba-nido-decaboran(10) - Herstellung, Struktur im festen Zustand und Stabilität(1) (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 2715-2724 
    Details
    ISSN: 0009-2940
    Keywords: Carbaborane, nido-C4B6, organosubstituted ; Carbaborates, fusion of C2B3, C4B6 dianion ; Carbaborane, C4B6, structure, phase transformations ; Calculations, ab initio ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Decaethyl-2,6,8,10-tetracarba-nido-decaborane(10) - Preparation, Structure in the Solid State, and Stability[1]The title compound 6, prepared in two steps from the pentaethyl-1,5-dicarba-closo-pentaborane(5) (1), is characterized at 103 K as the low-temperature solid phase LT-6 by a single-crystal X-ray structure analysis; 6 reacts with alkali metals (K, Cs) to form the C4B6Et10 dianion (62-) which is easily oxidized to 6 (e.g. with I2, FeCl2, HgCl2). Ab initio MO and IGLO calculations of compound 6 have been carried out.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911241212
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  • 9
    Electronic Resource
    Electronic Resource
    Chromophore Systeme, 1. Konformation und Lichtabsorption von Hexa-1,5-dien-3,4-dion (Divinylglyoxal) (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 821-826 
    Details
    ISSN: 0009-2940
    Keywords: α-Diketones, unsaturated ; Conformers, stable ; UV-Vis transition energies ; PE Spectroscopy ; 13C-NMR chemical shifts, correlation with dihedral angles CO/CO ; Calculations, STO-3G, MMP1 ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromophoric Systems, 1.  -  Conformation and Absorption of Light in Hexa-1,5-diene-3,4-dione (Divinylglyoxal)Divinylglyoxal (1) is investigated by several spectroscopic and theoretical methods in order to set up a correlation between the CO/CO dihedral angle and the transition energies in unsaturated α-diketones. According to the experimental (UV, IR, 13C-NMR, PE spectroscopy and dipole moment) and theoretical (ab initio and molecular mechanics) results, 1 exists predominantly as a C2h conformer (Θco/co=180°, ΘVinyl/co=0°). The dependence of transition energies on CO/CO dihedral angles is similar in shape to that for saturated α-diketones, but is significantly shifted to lower transition energies. 13C chemical shifts respond sensitively to CO/CO dihedral angles, and the ab initio calculated curve is supported by a few experimental results.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240423
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  • 10
    Electronic Resource
    Electronic Resource
    The Molecular Structures and Conformations of Bis(dichlorosilyl)amine and Bis(dichlorosilyl)methylamine in the Gas Phase: Determination by Electron Diffraction and by ab Initio Calculations (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 807-815 
    Details
    ISSN: 0009-2940
    Keywords: Amines, bis(dichlorosilyl) ; bis(dichlorosilyl)methyl- ; Gas-phase electron diffraction ; Calculations, ab initio ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase molecular structures of bis(dichlorosilyl)-amine, (HSiCl22NH, and bis(dichlorosilyl)methylamine, (SiHCl2)2NMe, have been investigated by electron diffraction and ab initio calculations on a MP2/6-31G* level. Because the latter suggest the presence of a mixture of two conformers for each molecule, attempts were made to fit the electron diffraction data in each case by two different models, one assuming the presence of only one conformation, and another allowing for two different conformers. The principal parameters (ra) from electron diffraction for (HSiCl2)2NH are (the appropriate ab initio calculated values are given in brackets []): r(Si-N) 171.9(2) [172.7], r(Si-Cl) 204.1(1)[204.5] pm; Si-N-Si 126.5(8) [127.4] N-Si-Cl 107.3(5) [110.8] and Cl-Si-Cl 106.5(3) [107.5]°. For (SiHCl2)2NMe: r(Si-N) 171.1(3) [171.5], r(Si-Cl) 204.0(9) [205.2], r(N-C) 149.7(10) [148.3] pm; Si-N-Si 124.9(13) [123.4], N-Si-Cl 109.7(5) [110.7] and Cl-Si-Cl 107.1(3) [107.2]° [110.8] and Cl-Si-Cl 106.5(3) [107.5]°. For (SiHCl2)2NMe: r(Si-N) 171.1(3) [171.5], r(Si-Cl) 204.0(9) [205.2], r(N-C) 149.7(10) [148.3] pm; Si-N-Si 124.9(13) [123.4], N-Si-Cl 109.7(5) [110.7] and Cl-Si-Cl 107.1(3) [107.2]°. For (HSiCl2)2NH three different conformers were found to fit the experimental data with the single-conformation model. In two of the conformers, the dichlorosilyl groups are twisted by Θ1 = 146.0(10)/Θ2 = 155.2(20)° and Θ1= 101.1(49)/Θ2 = 196.8(12)°; respectively counterclockwise from the positions in which the Si-H bonds eclipse the N-H bond. Both of these lead to nearly ideally staggered conformations of the two SiHCl2 groups when viewed along the Si-Si axis. In contrast, the third conformation is nearly eclipsed, with torsion angles Θ1 = 131.4(15)/Θ2 = 80.4(26)°. Planarity of the Si2NH group was assumed as suggested by ab initio calculation. For (HSiCl2)2NMe the experimental data could be suitably fitted by two conformers, in which the dichlorosilyl groups are twisted by Θ1= 161.8(13)/Θ2 = 63.1(23)° and Θ1 = 156.1(9)/ Θ2 = 177.1(15)° from the positions in which the Si-H bonls eclipse the N-C bond. The first of these structures has an eclipsed Si(NSi)Cl conformation and an Si…Cl nonbonded distance close to distance clse to the sum of the appropriate van der waals radii. MP2/6-31G* calculations support the GED bond lengths and bond angles of both molecules, but indicate different conformations for the most stable equilibrium geometries: the computed twists are Θ1 = 180/Θ2 = 180° and Θ1 = 177.0/ Θ2 = 183.0° for (HSiCl2)2NH and (HSiCl2)2NMe, respectively. Rotation about the Si - N bonds is a very facile process, cf. the computed [MP2/6-31G*//MP2/6-31G* + ZPE(SCF/6-31G*)] rotational barrier of 2.9 kJ. mol-1 for (HSiCl2)2NH.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951280812
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