Question

How can meso compounds be recognized?

Answer 1

By their symmetry.

Explanation:

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