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Solid angle as steric parameter of acyclic saturated groups
Author(s) -
Chauvin R.,
Kagan H. B.
Publication year - 1991
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.530030406
Subject(s) - steric effects , chemistry , ligand cone angle , steric factor , substituent , group (periodic table) , a value , envelope (radar) , cone (formal languages) , computational chemistry , crystallography , stereochemistry , geometry , organic chemistry , mathematics , telecommunications , radar , conical surface , algorithm , computer science
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.