(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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