Definition Steric strain

Pentacoordinate organocobalt(III) species have been suspected to exist either as reactive intermediates in ligand-exchange reactions [137-141] or, less commonly, as relatively stable species [140-142], Clear-cut demonstrations of stable 5-coordinate Co(III) complexes are relatively rare [136,143], One report contains two definitive examples of 5-coordinate complexes of the type Co(saloph)R (R = CH3 and /-C3H7) [136], Several interesting features emerge from these structures. First, the Co atom is displaced toward R. Second, the Co—C bond is shorter than in hexacoordinate compounds, but steric strain remains for z -C3H7, even in the pentacoordinate species. 

The interdependence of these conformational states and the possibility of transmission of conformational modification through a series of interdependent conformational states led to the definition of the gear-effect a conformational transmission, which is caused by interaction between polyhedral substituents and which depends on their polyhedral shapes. As a corollary of this definition, it was possible to outline the difference between the gear-effect and the classical buttressing effect (76JA2847). The two effects depend on different modes of minimization of the steric strain introduced by two... 

Stereoselectivity. See Asymmetric induction Axial/equatorial-, Cis/trans-, Enantio-, Endo/exo- or Erythro/threo-Selectivity Inversion Retention definition (e.e.), 107 footnote Steric hindrance, overcoming of in acylations, 145 in aldol type reactions, 55-56 in corrin synthesis, 261-262 in Diels-Alder cyclizations, 86 in Michael type additions, 90 in oiefinations Barton olefination, 34-35 McMurry olefination, 41 Peterson olefination, 33 in syntheses of ce-hydrdoxy ketones, 52 Steric strain, due to bridges (Bredt s rule) effect on enolization, 276, 277, 296, 299 effect on f3-lactam stability, 311-315 —, due to crowding, release of in chlorophyll synthesis, 258-259 in metc-cyclophane rearrangement, 38, 338 in dodecahedrane synthesis, 336-337 in prismane synthesis, 330 in tetrahedrane synthesis, 330 —, due to small angles, release of, 79-80, 330-333, 337... 

We have also proposed a general definition of the concept of stabilization energy applying to any compound, as shown by the numerous applications described in this survey article. Using this concept, we have been able to carry out a critical analysis and to offer a unified definition of various former notions such as hyperconjugation, resonance, ring strain, and steric repulsion energies. 

The use of the magnetic susceptibility exaltation as a measure of aromaticity has been advocated. The exaltation A is defined as the difference between the magnetic susceptibility and a sum of group increments. Although, like its resonance energy counterpart, this definition employs a fictitious reference system, the magnetic susceptibility is believed to be less sensitive to strain and steric effects than the total energy. Both and the index ... 

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