How can meso compounds be recognized?

1 Answer
anor277
May 4, 2016

By their symmetry.

Explanation:

A "meso"meso compound is a symmetric RSRS compound, with an internal plane of symmetry, such that upon reflection, the RR group maps onto SS. There are thus 2 chiral centres, with RSRS or SRSR configuration. To demonstrate the phenomenon, a favoured molecule is 2,3-"butanediol"2,3−butanediol, which has 3 stereoisomers, one of which is the "meso"meso. (Why does it not 4 stereoisomers: R,RR,R; S,SS,S; S,RS,R; and R,SR,S?)

If you have trouble vizualizing the symmetry or asymmetry, use a model. And do not be ashamed to do so. You have to (i) recognize the symmetry, and (ii) represent that symmetry on the printed page. Neither of these are trivial processes.

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