A short fragment of a polymer chain (four repeat units, end groups shown, substituents drawn with wedges) is drawn. Every adjacent pair of stereocentres has the same relative configuration (all substituents on the same side of the zigzag chain). How is this arrangement described?

ASyndiotactic
BAtactic
CIsotactic
DCis-tactic

Answer: C

When all the chlorine substituents of poly(vinyl chloride) lie on the same side of the main chain, i.e. every diad is meso, the arrangement is isotactic. Syndiotactic means alternating sides and atactic means random placement.

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