Pseudochiral carbon

The usual way to picture the configurational nature of a vinyl polymer is to consider the polymer backbone stretched out so that the bonds between the main chain carbons form a planar zigzag pattern in the plane of the paper and the X and Y substituents on successive pseudochiral carbons lie either above or below the plane of the backbone, as shown in Fig. 2.14. 

Answer Optical activity is influenced only by the first few atoms around an asymmetric carbon (C ). For the two sections of the main chain, these will be identical regardless of the length of the whole polymer chain. The carbons marked C in (Xlll) are thus not truly asymmetric and are termed pseudoasymmetric or pseudochiral carbons. Only those C centers near the ends of a polymer molecule will be truly asymmetric, but since there are too few chain ends in a high molecular-weight polymer such centers do not confer any significant optical activity on the molecule as a whole. Polypropylene is thus optically inactive. 

The stereochemistry of a particular chain is specified completely by the absolute configuration of every pseudochiral carbon. However, since enantio-... 

Such carbon atoms are referred to as pseudochiral centers in long-chain polymers because the polymers do not in fact exhibit optical activity (12). The reason for the lack of optical activity can be seen through a closer examination of the substituents on such a pseudochiral center ... 

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