Molecule atactic stereoisomerism

Stereoisomerism refers to molecular species that have the same composition and bond sequence but a different arrangement in space of their atoms. Stereoisomers that are characterized by different interatomic distances between certain atoms that are not bound directly are called diastereoisomers. Examples of diastereoisomers are cis-trans isomers of compounds containing C = C bonds and syn-anti isomers of compounds containing C = N bonds. Other diastereoisomers are not based on the presence of a double bond. For example, a molecule with more than one tetrahedral carbon that has different substituents may form diastereoisomers. For example, for a head-to-tail polymerized monosubstituted vinyl monomer, there are three possible structures indicated as isotactic, syndiotactic and atactic, which are schematically shown below ... 

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