CHAPTER 4: Question 9

3D Explanation

Monomer A is exactly analogous to the corresponding non-chlorinated compound discussed in the text. The O-Si and Si-C bonds in compound B are longer than the corresponding O-C and C-C bonds in compound A. This reduces the steric hindrance associated with the transition states for the interconversion of the helical conformations of the polymer and so allows the polymer to undergo rapid racemisation. In compound C, the phenyl rings are held away from the most hindered conformation, and this again allows racemisation to occur rapidly. 3D Diagrams of monomers A-C are shown below to illustrate the difference in the shape and size of the compounds.

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