(1R,3S)1,3-dibromocyclopentane (or 1s,3r?) and 1,1-dibromocyclopentane both have internal planes of symmetry but why is only the first one a meso compound?

1 Answer
anor277
Jul 1, 2018

Because by definition, a "meso compound" contains TWO potential chiral centres..

Explanation:

And of course a "meso compound" is an RS compound, such that it contains an internal plane of symmetry. And the goto example is "dimethylene glycol", i.e. H_3C-dotCH(OH)dotCH(OH)CH_3...the chiral centres are indicated.

Now such a structure gives rise to TWO enantiomers, i.e. "RR", and "SS"...and the "RS meso" structure...i.e. here RS-=SR...

For "1,1"-Br_2C_5H_8...THERE IS NO GEOMETRIC/STEREOCHEMICAL dimension to the structure. And certainly its mirror-images are superposable...

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