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  • 1,3-Cycloaddition, reductive  (1)
  • 13C-NMR chemical shifts, correlation with dihedral angles CO/CO  (1)
  • 51V  (1)
  • B4H8COendo structure  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Theoretical refinements of theendo and theexo structures of tetraborane(8) carbonyl (1993)
    Springer
    Structural chemistry 4 (1993), S. 1-4 
    Details
    ISSN: 1572-9001
    Keywords: B4H8COendo structure ; exo structure ; ab initio computation ; IGLO method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The molecular structures of theendo (1a) andexo (1b) isomers of B4H8CO have been optimized at the ab initio MP2(Full)/6-31G* level of theory. The agreement of the computed geometrical parameters with the recently published electron-diffraction (GED) data is very good, even though a number of geometrical constraints were applied in the experimental determination. The IGLO (individual gauge for localized orbitals)11B NMR chemical shifts, calculated at the II′//MP2/6-31G* level, are also in accord with experiment. The formation of1a and1b by association of B4H8 and CO is computed to be exothermic by 22.8 and 22.2 kcal/mol, respectively, at the MP2(Full)/6-31G*//MP2(Full)/6-31G* + ZPE(6-31G*) level of theory. The Lewis acid strength of B4H8 toward CO is comparable to that of BH3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00672092
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  • 2
    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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  • 3
    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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  • 4
    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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