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  • 13C-NMR chemical shifts, correlation with dihedral angles CO/CO  (1)
  • B4H8COendo structure  (1)
  • Chemical-shift computation  (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
    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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    Paper (German National Licenses)
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  • 3
    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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    Paper (German National Licenses)
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