Extra Figures of:
Carl Trindle: Entering Modeling Space. An Apprenticeship in Molecular Modeling, HYLE, 5 (1999), no.2
SHIELD is a rendering of a space-filling model of the co-catalyst Lewis acid with the ( S )-VAPOL ligand, bound as described in the text. The twisted (and chiral) black portion which wraps around the system is the VAPOL ligand. It prevents access by an enolate reagent to the aldehyde, which is bound to the chiral co-catalyst but blocked from our view. The orange bodies are a representation of bulky substituents on the VAPOL, which assures that its chiral ( S ) form is not easily interconverted to the opposite ( R ) form. ACCESS is a view of the other side of the co-catalyst complex with the reactant aldehyde  The aldehyde is close to the center of the figure, with the C=O fragment exposd.  The black VAPOL can be seen on the periphery but does not block access to the carbonyl carbon from this approach.
Copyright 1999 by HYLE and Carl Trindle (Dept. of Chemistry, University of Virginia, Charlottesville, VA 22901, USA; cot@virginia.edu)