Stereochemistry A Recap of Definitions

In 1951, the Dutch scientist J. M. Bijvoet developed a special x-ray technique that solved the problem. Using this technique on crystals of the sodium rubidium salt of (+)-tartaric acid, Bijvoet showed that it had the (R,R) configuration. So this was the tartaric acid studied by Pasteur, and racemic acid was a 50 50 mixture of the R,R) and (S,S) isomers. The meso form was not studied until later. 

Since tartaric acid had been converted chemically into other chiral compounds and these in turn into still others, it became possible as a result of Bijvoet s work to assign absolute configurations (that is, the correct R or S configuration for each stereocenter) to many pairs of enantiomers. 

PROBLEM 5.20 Show that frans-1,2-dimethylcyclopentane can exist in chiral, enantiomeric forms. 

PROBLEM 5.21 Is ds-l,2-dimethylcyclopentane chiral or achiral What stereochemical term can we give to it  

The correctly assigned (ff or S) configuration of a stereocenter in a molecule is called the absolute configuration of the stereocenter. 

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