Return to Contents Chapter 7 : Stereochemistry Ch 7 contents
What are stereoisomers?

Note that the term diasteromers is therefore quite general and other types of stereoisomers are subsets of the diastereomer group e.g. cis-trans isomers or conformational isomers

We will be expanding on some of these terms in the rest of this chapter.

The maximum number of stereoisomers with "n" chirality centers is 2n - due to the number of permutations possible.

Study Tip : note that stereoisomers have the same name except for prefixes that identify the spatial arrangement of the bonds :

  • cis- or trans-, E- or Z-  for alkenes e.g. cis-2-butene and trans-2-butene
  • R- or S- for optical isomers molecules (more on this later)
  • Questions

    Important properties of stereoisomers that you should know
    • Stereoisomers have the same molecular formula, and the same connectivity except for the arrangement in 2D or 3D space.
      For example, cis- and trans-but-2-ene both contain 2 CH3- groups, 2 H- and a C=C.
      Both can be represented generically as CH3CH=CHCH3 (i.e. same connectivity).
      But they are stereoisomers because the pieces are arranged differently in space.

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    organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary