PLANES AND CENTRES OF SYMMETRY

How can we tell if an object is chiral?  Obviously, we can envisage the mirror image and try to superimpose it on the original.  However, it is probably easier to look for a plane or centre of symmetry.  If one of these elements can be found, the object is definitely achiral and will be identical with its mirror image.  Propanone (acetone; below) is a good example of a molecule with a plane of symmetry.
 

Meso-CH₃CHOH-CHOHCH₃ also possesses a plane of symmetry in one of its accessible conformations.  However, the conformation featured on page 7, repeated below, is an example of a structure with a centre of symmetry.
 

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