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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: steric effects ; geometric model ; ester hydrolysis ; ester conformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030406
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: samarium di-iodide ; divalent samarium ; samarium dicyclopentadienide ; phosphine oxide ; Michael additions ; diphenyl alkyl phosphine oxide ; phenyl dialkyl phosphine oxide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590090510
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    Paper (German National Licenses)
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