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#1 2010-04-14 10:33:15


stereoisomers of hexachlorocyclohexane


I have a doubt on the definition of Meso Compound. For a compound to be classified as a meso compound, it must have chiral carbons and must satisfy a symmetry condition (plane of symmetry or center of symmetry). In the adjoining figure, we can see some of the stereoisomers of Lindane which have to be classified as chiral and meso compounds.

Structures 2,3,4,5 and 9 have a plane of symmetry and they have chiral carbons - this implies they are meso compounds.
Structures 7 and 8 have chiral carbons, do not satisfy any symmetry condition and are infact mirror images of each other - therefore, they are chiral (enantiomers).
Structures 1 and 6 do not contain any chiral carbon though they satisfy symmetry conditions - therefore, they are achiral compounds but is it correct to label them meso compounds ?

Thanks and Regards,



#2 2010-04-15 00:34:01


Re: stereoisomers of hexachlorocyclohexane

Meso compounds are a special type of compound with two or more chirality centers. Normally, one would predict that if a compound had two chirality centers, then 4 isomers of it could exist. However, if the compound has a plane of symmetry, then the mirror image of a compound may result in a single compound.

If you draw the mirror image of (2), you will get (2). Hence it is a meso compound. If a compound does not contain a chirality center, then the mirror image of it may give the same compound, cyclohexane, benzene, (1), or (6).



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