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  • 1
    Digitale Medien
    Digitale Medien
    Solid angle as steric parameter of acyclic saturated groups (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 242-253 
    Details
    ISSN: 0899-0042
    Schlagwort(e): steric effects ; geometric model ; ester hydrolysis ; ester conformation ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: With the early aim of quantifying steric consequences of chirality, efforts to define a nonempirical steric parameter of chemical groups are reported. Steric hindrance of a reacting center by any acyclic saturated R group has been characterized by a geometric “axial steric parameter”: the solid angle of R. When the group is a “symmetric top substituent” (i.e., when all the terminal atoms are equivalent), the solid angle matches the solid angle of a cone envelope of R. The definition of this cone is compared with Tolman's definition of a ligand cone in organometallic complexes. The chemical significance of this parameter is shown by an excellent correlation with the Dubois' experimental steric parameter E′s. Modeling steric repulsion by the cone of R, and correcting solid angles for conformational effects, only 3 empirical coefficients are needed to calculate 33 values of E′s with less than 10% error. The cone model is suggested to be relevant within the limits of random and independent free rotations about all the bonds in the C-R group. A separation between “axial cone steric hindrance” and other steric effects is proposed. The basic model and the corrections proposed allow the conformational features of esters to be discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chir.530030406
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  • 2
    Digitale Medien
    Digitale Medien
    Circular dichroism studies of an elastin crosslinked peptide (1976)
    New York : Wiley-Blackwell
    Biopolymers 15 (1976), S. 833-841 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Circular dichroic studies of a desmosine crosslinked peptide reveal a hitherto undescribed elastin spectrum possessing a weak negative band at 230-235 nm, a weak positive band at 215 nm, and a maximum negative band at 190 nm. The spectrum is sensitive to both pH and temperature displaying increased ellipticity of the 215-nm band at acidic pH and low temperature. The general shape of the spectrum and its behaviour toward temperature changes suggest the presence of an extended helical conformation. Susceptibility of insoluble elastin to digestion with chymotrypsin is increased tenfold at low temperature (4°C), supporting the contention that the conformational change of the type described above occurs in insoluble elastin. Such changes in conformation would result in increased availability of aromatic amino-acid resiudues to peptide bond cleavage.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.1976.360150503
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  • 3
    Digitale Medien
    Digitale Medien
    Complexes with Chiral Alkylcyclopentadienyl Ligands for Homogeneous Catalytic Asymmetric Hydrogenation of 2-Phenyl-1-butene (1979)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 18 (1979), S. 779-780 
    Details
    ISSN: 0570-0833
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/anie.197907791
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  • 4
    Digitale Medien
    Digitale Medien
    Komplexe mit chiralen Alkylcyclopentadienyl-Liganden für die homogene Katalyse der asymmetrischen Hydrierung von 2-Phenyl-1-buten (1979)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 91 (1979), S. 842-843 
    Details
    ISSN: 0044-8249
    Schlagwort(e): Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/ange.19790911012
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  • 5
    Digitale Medien
    Digitale Medien
    Synthesis of tertiary phosphine oxides mediated by SmCp2 or Sml2 (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 9 (1995), S. 431-435 
    Details
    ISSN: 0268-2605
    Schlagwort(e): samarium di-iodide ; divalent samarium ; samarium dicyclopentadienide ; phosphine oxide ; Michael additions ; diphenyl alkyl phosphine oxide ; phenyl dialkyl phosphine oxide ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tertiary phosphine oxides are prepared under mild conditions by sequential addition of diphenylphosphinoyl chloride to divalent samarium compounds (SmCp2 and SmI2) followed by reaction with various electrophiles such as organic halides, tosylates, epoxides or α,β-unsaturated ketones. Biscyclopentadienylsamarium (SmCp2) gives better yields than SmI2. Similar reactions, using phenylphosphonoyl dichloride, SmI2 and subsequent addition of two equivalents of activated halides, yield the corresponding tertiary phosphine oxides.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aoc.590090510
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